I prefer a backpack as it keeps the load centered over both shoulders, as opposed to slung over a single shoulder (messenger bag, dad bag, traditional diaper bag, whatever)... Some diapers, a few wet wipes, a snack or two, a bottle and a bit of milk doesn't sound like much, however... Remember when you went [somewhere] and asked your wife to hold your keys/wallet/sunglasses/SOMETHING in her purse? Well, now YOU are the pack mule and your all saddled up. She will see that bag and not be happy until you are carrying EVERYTHING! Also, while we never sprung for one, the frame packs that are kid carriers with under-storage for diapers and such are GENIUS! It never failed that I would wind up carrying the diaper bag and the kid (we have 2 now) by the end of a day out at the zoo/aquarium/park/store/wherever. I would also steer away from a tactical bag if only because they tend to be spendy, tend to draw attention, and a diaper bag has a high likelihood of encounters with old milk, dirty diapers, and used food wrappers. My last piece of advice is buy something you will use after the kid is out of diapers. We are still using the [third] "diaper bag" we bought with our first son- almost 8 years later. The first was one of those you will never see a guy carrying. The second was better but uncomfortable. This one is a laptop pack that has plenty of pockets and pouches for snacks/drinks/sunblock/spare shirts on the weekend (no more diapers here, suckers!!), but also does double duty carrying laptops and work stuff during the week.
