Like most of the responders on this thread, I set my pack down to get to my LF gear. For keeping your gear out of the mud, another option is to get some of the polycro groundsheets from Gossamer Gear. They're light and inexpensive, and reasonably durable given their weight.

I'm probably going to get some of the Photobackpacker lenses cases and such, even though I don't use one of their backpacks. I think they'll help with organizing my gear so that it's more accessible. At least, I hope so. I don't ever attempt to use my LF camera without putting my pack down though, since it has both my camera and my outdoor gear (layers, shell, gloves, light, stove, shelter, sleep stuff, etc).