I've got an A5 trifold kneeboard which contains everything I need to go flying, except the headset. (I fly aerobatics a lot, in a rented plane, and taking a flight bag with all sorts of stuff is not a good idea. So I leave that on the ground.) So essentially all I need to grab is this kneeboard, my headset and some personal items (watch, sunglasses, spare glasses) and I'm legally and practically speaking ready to go.
"Everything I need" that is contained in the kneeboard is:
- License
- Flight computer, ruler, protractor (I know, not strictly needed but that's where I happen to keep them)
- Map of the local area
- Plog and relevant approach/airport plates
- Some spare bits of paper to note tacho/times etc.
- Pencil
- Checklists
- Some aeros specific items such as the sequence and some means to secure this (rubber band around my leg).
In-flight I usually do everything from memory (local flights) or I simply take out the metal insert containing the plog and approach/airport plates, the pencil and the relevant map. The rest of the kneeboard then gets stored somewhere secure but in reach.
In general, in the course of your flying career you will notice that less is more. When you prepare your flight properly the amount of paperwork and other items you actually do need in-flight is really very limited. Don't go overboard with a minimalistic approach though. Make sure all you need to do a diversion is somehow within reach. But that doesn't necessarily have to be on your kneeboard.