For Harrison... we have about 5 nappies, wipes, nappy poo bags, hand cleaner, a muslin (mainly for use as a change mat) 2 spare changes of clothes, 2-3 bibs, 2 dummies, and I usually grab a piece of fruit like a mandarin or similar... and some crackers and cubed cheese before I go anywhere.
Being that Harrison is older, I can usually grab him a sandwich while I am out, but I like to have some healthy-ish foods for him to much on too... mandarins are a fave as they're easy to peel and break into portions.