In my bag I have:

Bibs (and loads of them!)
Spare set of clothes x 2
1 or 2 Toys
Cloth Nappies which is use for burping etc
Bunny Rugs x 2
Baby Wipes
Nappies x 8
Botty Butter (Tasmanian-made non-petroleum based cream for bottoms!)
Face Washer
Other wipes for cleaning hands etc
Jacob's 'Blue Book' (Health Record Book)
Plastic Bags for dirty clothes/bibs
Nappy Sacks for dirty nappies
Changing mat
Dummy x 2
Insulated Bottle Bag (with bottles, formula etc).

I *think* that's about it LOL. We also have a spare bag in the car just in case we dart out without taking the main bag, and that contains all the basics, not everything on the list that is in our main bag. I also usually take one more bottle with me than what I think I will need, just in case.

My bag also has a section for my things, like wallet, phone, keys etc which is great. Depending on the day I might also throw in another hat or a blanket etc. Oh, and my motto always is "when in doubt, take 2" and by that I mean at LEAST 2 LOL!!!