Openings commonly found in an U1600 section?

Any of them?

I find that people play different things depending on location. Sometimes the players in an area will mostly play the same stuff and sometimes they all play different things. I don't think you can really prepare that well unless you know exactly who is going to be there and can find a bunch of their rated games online somewhere.

Queens gambit-mostly declined

I have found huge success in the Kings Indian attack/defense. Also, I have beaten 1700 uscf at tournament with the scotch gambit! Look into that one! It has lots of very sharp tactical positions that u get into. Good luck!

d4 and bishop fienchettos will woke very well, as they have for me. e4-Ruylopez Berlin variation. Lots of french and Sicilian narjdorf variations. Know your openings. Really, if you know basic development strategy, there's no need to memoriz openings, plus openings are only a 1/4 of the game, Develop and centralize... King safety...etc.