On my bike, a small Specialized, I've got one water bottle mount, and it is very important that it be usable to me. In our hot summers, I like to fill it with an energy/electrolyte drink. I leave the camelbak for water only. So I've been using the Arundlel Side Loader cage. I can get a large camelbak Podium bottel in there, and it pulls out straight to the side.

As for tools, gosh I can't find one that works well all around. The CB-17 has a good selection, but the chain breaker sucks. So I also carry an old Bontrager mini tool that has a great chain breaker. Then I throw in a Park MT-1 tool (great allen key tool), tire irons and a patch kit. I keep a micro tool with a mini pliers in my wallet at all times so that is also with me on my MTB rides. Overkill? I donno, I've used them all at one point or another so the are not just dead weight. If I found the perfect mini tool I could narrow it down, but I don't think it exists.

Shin guards and elbow pads look silly. But I wear them all the time while MTBing. It's already saved my skin- I crashed hard doing a superman when my bike jammed into something buried in soft dry sand while I was turning at speed. While I did bruise my ribs bad, I didn't lose all the skin from my elbow or slice open my shin. I use FOX knee/shin guards, and the awesome 6 6 1 EVO elbow pads.