Truk has a "dive store" but not in the essence that you might be used to. It is basically a clothing retail store. So you can buy 100 different Truk T shirts. But thats about it.
So ensure that you are bringing ALL the kit you need. They have single tank gear for hire.
Make sure all your regs are well serviced before you go.
Plenty of Light!!! Bring at least 2 good dive lights as there are many great peneration dives and millions of dark places to explore. You dont want to jeopardise your safety by only having one small dive light.