In the time frame we are concerned with, a few days, tooth care is not of high importance. But if you have the room, some basic tooth hygiene is worth considering, particularly if your mouth health is a bit weak. Although a few days (or even few weeks) without tooth care won’t kill you, it might encourage dental problems.
Perhaps the easiest thing to include is some floss. Not only is this compact and inexpensive, but it has uses other than caring for your teeth. Basically, it can be used as string, or fish line, or thread. Perhaps the most compact way to carry floss is a “FlossCard” (www.flosscard.com), a credit card sized floss dispenser. Or, you can just get a standard dispenser of floss (I prefer the 100 yard ones, even for daily use), break it open, and take the small spool inside for your kit.
For the tooth surfaces, a toothbrush is handy; particularly a folding one. There are ones which fold, and ones which push together. The folding ones have worked better for me. My favorite is one I got at a medical supply store which has some “flossing” filaments among the bristles. There are even some travel toothbrush sets which include a small tube of toothpaste; I would not waste any space or weight on toothpaste, or risk it being damaged by heat, or leaking. Toothpaste is not a critical survival need, at least not in the short term.
Finally, if you need them normally, an “interdental” or “christmas tree” brush would be appropriate. If you don’t know what these are, you probably don’t need them (or need to change to a better dentist). If you do want to include some, the best choices are the “travel” ones. They are quite compact, and with care, can last for several uses. They are available in cylindrical and tapered (hence “christmas tree” brush) and in various sizes for various sized gaps between teeth. I prefer the largest tapered ones, as my rear teeth are the problem area. If you are not used to them, get a selection and try them out, to see which fit, and which last the longest for you.