ORIGINAL: piper_chuck
I use microbaloons. They work with either CA or you can mix them into epoxy. It's a handy way to add a fillet to make a stronger joint or to fill gaps.
For us cheapskates you can use corn starch instead of microbaloons. Two reasons to mix with your epoxy. 1) it keeps the epoxy from "flowing" out of the gap you're filling. 2) it makes the epoxy very sandable and easy to finish out. One note is that you should never use epoxy to "fill" a structural joint. You should always go for wood-to-wood contact when you are building as it gives the strongest joints.
Hope this helps
Ken