For writing there are 4 things I like to use/have in my bag:
1. Space Pen, as it writes on most surfaces, doesn't leak, ect.
2. Pencil, as it can be erased and if need be burned
3. One of the two sided Sharpies, these sharpies can write very small and quite large on most surfaces and can withstand bad weather for a while once dry.
4. Sharpie Industrial, best sharpie ink ever. Much more perminant and wear resistant then the regular sharpie, however without the second tip it writes too large for pen use. If they made a twin tip Sharpie Industrial I'd be the first in line to buy some. <img src="/images/graemlins/grin.gif" alt="" />
In my pocket kits I keep a pencil as it can handle most writing needs, is small, and can be used as tinder. I like that the best for there since space is a minimum. For my bags or fanny pack sized kits I try to fit in the above, as it covers basically every writing task I could think of.