Wasabi has a "hot" like horseradish, because that's what you're getting in most preparations - horseradish with some added flavor and color. The actual wasabi root is ungodly expensive here in the US. I paid $60/lb for it, about $15 for a small piece that looks like green ginger. It's much more aromatic than the "fake" wasabi and best used in very small doses.

If you just want a shot of the wasabi flavor, see if your store carries wasabi-flavored peas. They go well in GORP, but the intensity of the burn decreases the longer the peas are exposed to air, so add them just before you use the mix.

I personally like spicy food, so when I found a take-out restaurant that had packets of Tabasco and picante sauce, I hoarded a small sandwich bag of them over several months. Alas, the packaging isn't very durable, and I recently threw out most of them, as the contents were eating through the plastic! So now it's back to using little squeeze bottles until I can find another reliable source.