i tried putting some lenses in here's what it can hold..
Front left and right - Spare Batt/ Filters/ CF Cards
Front lower left and right - Kit lens/ SB800/ 50mm prime Lens (there's space).
Rear pocket - towel (Camo sheet for birders or cap) or another lens (70-300) if you want.
Strap (hanging down) u can attach something to that little loop. It's secure. Im gonna use it to Khao Yai national park if my finger gets well... got whacked on my trigger finger while playing basketball just today.