All that I really need to go geocaching is my GPSr and a pencil, but I often take a little more than that.
I have a small pocket-size bag that I take with me, and it has mostly everything I need for any geocaching adventure, whether it is a walk through a local park or up a mountain trail.
My Geocaching Bag -
This is my "take to every cache" geocaching bag. Nothing special, nothing fancy; just a plain nylon bag with a zip-top.
There are two things that I really like about this bag:
1) It is small enough to fit into a pocket.
2) It has everything I need to go geocaching.
The Inside Goods
1) Geocache-Bag - It would impractical to just put all of this stuff into my pockets.
2) Ball-point Pen and Pencil - I strictly adhere to the tenant that a geocache is not officially found unless I sign the logbook. Therefore, I always make certain I have at least two ways to scratch my mark. Ball-points tend to write on all types of paper, even when wet, and a back up pencil works in the colder weather I experience for a good portion of the year.
3) Extra Log-Sheets - Again, officially a geocache isn't found unless the logbook is signed, so I bring a few extra sheets along just in case I run into a logsheet that is just too full to fit my signature or needs to be replaced.
4) Signature Items (not shown) - Mainly pathtags and/or business cards; I only put these in geocaches that I really like or feel are a great example of what I feel is a true high-quality geocache.
5) Extra Batteries - The Foretrex101 must be fed.
6) 120-Decibel Whistle - Because I often geocache by myself, I carry this item just in case I fall and need to signal for help. (Has never been used!)
7) Garmin Foretrex 101 - Super-basic GPSr, but it has been with me since the beginning and has led me to every geocache I have ever found.
8) Metal Pencil Sharpener - Sometimes I come across geocaches that need their resident writing utensil sharpened in order to actually function. Metal is much more durable than plastic (This was originally a trade item too.)
9) "Hooked" Safety Pin - Most of my items are self-explanatory -- except the safety pin. I heard about these neat little tools from Sonny on the PodCacher podcast. It is simply a basic safety pin with its tip bent slightly with a pair of pliers. Closed, it just hangs out in my bag, but when I come across a very snug micro- or nano-cache, the pin can be opened, inserted through the center of the rolled-up logsheet, "hook" the bottom edge, and pulled up with the whole piece of paper to sign.
10) Notebook - As a "traditional" geocacher I tend to make notes about geocaches that I either would like to find, puzzles that I have solved, or required logging information for Virtual and Earthcaches.