I list everything by category, then with options (best, bulkiest to smallest, most compact)
1. Water Storage (nalgene bottle, collapsible canteen, gerber milk baggy)
2. Shelter (Bivy sack, large garbage bag, space blanket)
3. Signaling (EPIRB, signal mirror/whistle, cell phone) *
4. Water Purification (water filter, micropur tablets)
5. Tools (Folding knife, leatherman, scalpel or xacto blade)
6. 550 Cord (50ft, 20ft, 10ft)
7. Fire (sparklite kit, bic lighter, waterproof matches)
8. Tool (headlamp, LED flashlight, keychain flashlight)
9/10 Medical (israeli bandage + iodine / Medical Tape + gauze roll / duct tape + gauze
Now that I've gone through this, I'm not sure if a "top ten" list is actually a useful way to start. The goal isn't to hit a number of items target, but a weight/bulk target.
Plus, the scenario is limiting, too. The three scenarios that I can forsee myself being in are: disaster / bug-out, travelling accident, and every-day accident. A bugout bag, car pack and my EDC each fill different but overlapping roles.
One thing that this exercise does help with is reminding us that gear can serve multiple purposes. And that's useful to remember, since while nicely packaged solutions for, say, fire are nice, ingenuity and experience can make up for weight and bulk any day.
* I list the cell phone as most compact since people who have one are carrying it anyway.