I was just jamming over a chord progression and wondered what I would use for 3 note tapping. The progression is just A5 C5 G5 A5, each chord lasting one bar. What notes would I use for tapping over 4 bars using this chord progression?

Even though the chords are power chords, it's safe to assume that the A is a minor and the C and G are major chords.

The most obvious note choices would be the notes from each chord:
Am: A C E
G: G B D
C: C E G

if you want to stay on one string, you can play something like:
e:-12-5-8-12-5-8-12-5-8-12-5-8 (Am)

e:-12-3-8-12-3-8-12-3-8-12-3-8 (C)

e:-10-3-7-10-3-7-10-3-7-10-3-7 (G)

Of course, you can include other notes, and make more inctricate tapping patterns, etc.
it really depends on the emotion you want to convey but i woul arpegiate ot some cnords like sus2 maj7 min min 6 not in any specific order thats for you to find but to give you ideas to run with

sus2-1 2 5
maj7-1 3 5 7
min- 1 b3 5
min6-1 b3 5 b6