On my WR, I had a small tool bag on the rear fender and I always had channel locks and a spark plug, A "husky" t-wrench that fit an 8 and 10 mm socket in the handle (for pulling off plastics), zip ties, and a small spool of bailing wire. For 90% of my quick fixes, these did the trick, and I liked it because I didn't need to take off my pack to change my plug or zip tie on a loose something-or-other.
In my pack I had water, needle nose pliers, a crescent wrench w/ some duct tape storage wrapped around the handle, A pack of various metric dirtbike bolts (I can't count how many times this came in handy for me or a friend), granola bar, gun, knife, and a cheapo blue tie-down strap (this also came in handy many times for various things including towing.)
I never really needed anything else. I've never gotten a flat out on the trail, so I haven't worried about a tube. (I'm glad that didn't ever bite me in the butt!)