This is something that I put together recently. It has all of the items needed to play guitar, so it is a good thing to have when you go places. Mine is great for trips to the local guitar store, or just to keep things organized in my room.
Step 1: A Tuner
A tuner is needed if you want to keep your guitar sounding its best. There are hundreds of different tuners available to buy. Mine just happened to fit in my Victorinox tin.
Step 2: Picks, Picks, Picks!
A guitar pick is always a god thing to have. Unless you play using fingerpicking, it is a necissity. It allows you to strum the strings, making the sound. Plus, they take up little space, so you can cram quite a few of them into the Voctorinox tin.
Step 3: A Good Capo
To find a capo that fits in the tin along with the other items may prove difficult. They sell wraparound (not spring powered) capos at Best Buy, or you can go to your local guitar store. The capo in the picture is around some guitar toy thing. A spring powered capo will not work, as it is too big to fit in the tin.
Step 4: A Cleaning Cloth
A cleaning cloth is good to have, but it is not necessary.