I take the smallest bag/backpack possible, but have found that if I group things in smaller bags, it's all easier to locate when needed.
I have a fabric zipper-closed wallet (from the China pavilion in Epcot) that holds my license, insurance card, KTTW card (not anymore

), credit card, and some cash.
I have a slightly larger fabric bag that holds moleskin, small manicure scissors, emery board, small nail trimmer, blister bandaids.
Another fabric bag holds our meds: Some ibuprofen, extra strength tylenol, and alleve in one small prescription bottle. I have 'blister sheets' of some meds so take along 2 or 3 'bubbles' of sinus pills, Immodium, bonnie, antihistamine, and DDs inhaler.
Also in the bag are frozen water bottles (or just a few empty ones to pour QS water into), ponchos (squooshed down into a ziplock bag), sunscreen, and a sunscreen stick (for noses/lips). If we are traveling in the summer/really hot times, I have an insulated lunch pack (fabric) that I carry the water bottles in, as well as some wet, frozen wash cloths. Everything stays colder that way. The last couple of trips we've skipped the water bottles and just gone with what we can get from QS, but I miss having a cold drink in a long line.