I'd go with either reflective or glow-in-the-dark tape, depending on your venue. If there'll be lots of bright lights, go with the reflective tape (I have a small reflecting stripe on the running tights I skate in, and in any pictures of me with flash, the stripe appears to glow). if it's more likely it'll be dark or there'll be black lights, go with the GITD tape. Check the flexibility of whatever you get, though. I'd start with the fabric store or a running supply store before the auto parts or police supply stores; the former will have stuff actually meant for fabric, the latter will be meant for autos/bikes/etc. and will be more stiff and might not flex so well as you move. Also less likely to wash well.

You could try to find something self-stick, but you might be better off either sewing or using that "liquid stitch" stuff that is like glue for attaching fabric together. Then you'd know it's really stuck down and you wouldn't have edges peeling up. You probably want to draw lines on with tailor's chalk first-- check this both with the garments off AND on to make sure it'll lie the way you want. Measure twice and cut once. Etc.

If you go to the fabric store, ask their advice unless you or someone who will be helping you knows a lot about sewing. They might have some good ideas, or tips/potential problems you didn't think of.

Oh. In that case, workout gear. Running tights and a long-sleeved tech top. Unless you wanted to look more like the Club programs.

In that case, you'll need to look into cyberpunk. Or maybe Hot Topic sale rack.

Come on guys, where are the ideas???

This is only for a Castor costume now!!!!