I am here for you, Parents of the Internet. I am here.
The answer depends a lot on the age of your baby/ies, how many of them there are, where you're going, how long you'll be there, and what you'll be doing.
For everyday outings, though, to the store and whatnot, you need the following, minimum, no matter what the age:
With two kids in them, I tote around a lot of diapers. A lot. The best rule of thumb I've found is to take 2 diapers for every 4 hours you plan to be gone (minimum number of diapers per kid = 2). I use a gallon sized Ziplock bag to keep them from getting all bunched up in the bottom of my bag. I can also squeeze out the air, so they take up less space.
I always take too many diapers for overnight trips. When you take a full package, they're nice and compact and squashed together, and you don't have to worry about running out.
You can never have too many wipes. They're not just for butts. (That should totally be their slogan - "Pampers Wipes! Not just for butts!") They are handy for wiping hands and faces, cleaning up spills, cooling off a hot kid, cooling off a hot mama, and about ten zillion other things. Trouble is that pre-moistened wipes get heavy. A brick of wipes weighs as much as, well, as much as a brick.
I carry a "diaper bag sized" hard case in my bag, with 10 - 20 wipes crammed in it (I refill mine) and then I keep a full sized box of wipes in the car, because you never know... You just never know.
I don't know what it's like where you are, but it's hot and muggy in Indiana. Maybe it's just my kids, but nothing gets them fussy faster than being thirsty. If we stopped at McDonald's for a chocolate milk or a pop every time my kids get thirsty, we would rapidly go broke. I don't leave home without sippy cups. It's cheaper. It's environmentally friendlier. It keeps my kids from losing their tiny minds. I will take a quick trip without diapers, say to the pharmacy when they've just been changed, but I never go anywhere without sippy cups. I even keep extras (those thin plastic take and toss ones are a good choice for this) in the car, because it's cheaper to buy one big drink and divide it than it is to buy a bunch of little drinks. And Claire hasn't quite mastered the cup and straw.
Kids have very little patience for waiting in line, running errands, and grocery shopping. That's why every good diaper bag has a few distractions in it. Crayons are good. I keep a bunch of Happy Meal toys (espeically those with wheels) in mine - they're small, they're light, and no one is going to need therapy if we lose them. My kids also love Tic Tacs, so I've been keeping those in the bag lately (I'm aware that they're a choking hazard, but if it buys Mommy 3 minutes of peace before Claire starts saying, "Mo! Mo!!" then it's all good). Mommy's iPod is also a good distraction. One of my Tweets today was that the kids' song to Mommy's song ratio on my iPod is about 7:1. That makes me feel so old. It's good to rotate your distractions regularly, because no kid is going to be entertained by the same Hot Wheels Happy Meal toy for 3 days in a row.
Snacks are also a good distraction. Keep it healthy with the individual boxes of raisins. We also like the fruit snacks that come in packages of 10, even though they're not fruit. 100 calorie packs are the big thing, lately, and they're just about right for a kid-sized snack, too.
"It can't be that simple!" I hear you say. "This bag I bought has 10,000 compartments - I can't just need four things!"
Well, of course, if you're bottle feeding, you'll need the bottle stuff. If you're going to be gone during a meal, you'll need food and/or utensils. Maybe a bib.
And some of the pockets can be for your stuff, eliminating the need to carry a baby, a diaper bag, and a separate purse.
But I promise, that's all you really need, if you have a car.
I keep everything, and I do mean everything, in big plastic totes in my car. I have extra toys, books, a first aid kit, infant and child formula medications, bungee cords, sun screen, emergency food, a small fire extinguisher, and about 10,000 other miscellaneous things. I would rather trek back to the car to grab something I need, occasionally, than become a hunchback from carrying everything I could possibly ever need all the time.
That said, there are things that I've found that are handy to have on hand, if you still have room in your bag (or car):
- "Feminine products" (I stick mine in the Ziplock with the diapers)
- Handy Sacks - you can find these at Walmart in the check out lane, they're blue, it's a little bag, about the size of a graham cracker, that has plastic bags inside it. These are really handy for stinky diapers
- Hand sanitizer
- A small tube of sunscreen (or buy a big one and get a refillable travel sized container, save money, less waste, cheaper)
- Off makes insect repellant wipes. Those have come in handy.
- A small notebook or Post-It Notes and pen to combat Mommy-brain
- A baby nail trimmer (because sometimes they fall asleep in the car seat, and you can get 'em while they're unconscious and avoid all the screaming)
- Orajel, or whatever you use for teething pain
- A nail file (no MacGyver use, here, I just always seem to need one)
- A nasal aspirator (or nose-sucker), if your baby is small and/or stuffy (we got caught without one of these, once, and while I'm not going to tell you what I did to fix the situation, I can pretty much guarantee that you don't want to kiss me on the mouth ever again
- An umbrella
- A sling (oh, I loved my slings, and I am so sad that Claire has outgrown them. They were so easy and so handy and so cozy)
- A camera (I traded in my DSLR for a pocket-sized point and shoot so that I can have it with me all the time)
- Cell phone (is there anyone left who doesn't have a cell phone? Certainly none of the parents I know!)
- Spare keys because kids love to play with keys but you don't want them to play with your real keys because they tend to drop them down sewers so give them all those anonymous keys that every junk drawer has, on a pretty keychain, and just calmly wave bye-bye if they go down the hole
- Address book/PDA/etc. our phone company puts out a small yellow-pages-only phone book that is so handy - it lives in my car
- List of emergency numbers (if you don't have an address book/PDA, at least write down all the important numbers in your life and carry it with you, so that if something happens, you don't have to rely on your memory when you're under stress)
- Medical info. Mary Grace is allergic to amoxicillin, for example. That's pretty easy to remember, even with Mommy brain, but if you have more than one allergy to remember, maybe you should write them down. You know. Just in case. Check these out for the emergency numbers/medical info. I think they're so cute, and you can make your own.
"But Amy," you cry, "I live in the big city! I walk everywhere! I don't have a car to use as a giant diaper bag!!"
Well, ok, you're hosed. You're just going to have to suck it up and carry the industrial sized duffel bag diaper bag. Maybe you should make like a flight attendant and get one of those wheely suitcases. At the very least, you want to get a good stroller that has a bin underneath for carrying stuff, otherwise you're going to break your back. I take the stroller along all the time, but the kids are rarely in it. I use it like a grocery cart, to haul all our crap. I'd rather carry my kids than my junk, right? And if we have a stroller with us, I always know where everything is. And it has cup holders. I have the Graco Travel System thing (with the infant bucket and the stroller) and it has served me well through two kids, and I love it.
The good thing about being in the city is that there is always a drug store or something nearby, so you don't necessarily have to have everything on hand that you would need for a walk through the desert or something.
What am I forgetting? What do you have in your diaper bag?