First of all, I'd bring the tripod and all my lenses, etc ON the trip with me. That way, at least if you get out and decide you wish you HAD the tripod, you can bring it with you the next day.
Like one of the other posters above, I don't actually HAVE gobs of gear to take or leave, especially when it comes to lenses.
I have four lenses, and I generally take them all with me.
When I go out for a day of shooting, especially if I don't know for sure what I might be getting into, I take my LowePro 202AW sling pack--it's small, but holds a surprising amount of stuff. I also take a fanny pack.
In the LowePro:
D7000
70-300 lens
Tokina 100mm macro
50mm f/1.8
18-55 kit lens (yes, I still carry my kit lens. Get over it.

)
Flash with extra batteries
Extra camera battery
Remote release
Extra cards
Other little items: notepad, pen/pencil, two trash bags, gear twist-ties
In the fanny pack:
Two bottles of water
Snacks (usually either nuts, craisins and/or granola bars--easy to carry and good pick-me-ups)
Once I get out and start shooting, one of the lenses usually ends up in my fanny pack. That way, I have really quick and easy access to two lenses--the one on the camera and the one in the fanny pack, and it also lightens the load on my back.