While putting together a First Aid kit for Matt to take with him on his mission, I put together a mini one for him to keep in his back pack or shoulder bag. Odds are that if he's going to get hurt it will probably be while he's out and about. If he's going to get sick (besides indigestion or a headache, that is) it will probably be while he's at home and sleeping. That gave me a pretty good idea of what I needed to include in the mini kit.
I used the same style of container that I used for his regular First Aid kit...just smaller. I found it at the office supply store for less than $1. It measured about 3.5"W x 2.5"D x 2"H. I love the clip that comes up the sides to hold the lid in place, should keep things together at the bottom of his bag where they can be found easily if needed.
Make sure to include a few band-aids (the fabric kind will stay on longer), some alcohol or disinfectant wipes, some moleskin already cut to size (for the occasional blister that may arise on their feet), some aspirin or Ibuprofen for pain and something to settle their stomach. I used some small bags that I have around for making jewelry. They can be found at the craft store where you can buy them by the box or ask for them at the bead counter and purchase them by the piece. Make sure to label each bag clearly.