I did this flight last week. It is amazing how sleepy SFO gets after midnight aside from the late Asia departures in G. No concessions in A are open other than the duty free shop.

As mentioned above, the only realistic lounge option is the UA Club in G, which closes at 1am and requires either a long walk behind security or doing security twice. The UA Clubs in E and F close even earlier. I initially was maybe going to try the AC MLL in T2 and walk to A afterward, but I was a little shocked to look up beforehand that it closes at 19h15.

If you're local to SFO, my advice would be to nap and take a shower at home and arrive as close to the flight as possible. The Copa flight is basically the only departure in the entire International Terminal at that hour, so there's no line at security. I also found Copa's policy of setting the boarding time at 60 minutes for a 737 to be a little silly.