3.4 timing belt kit has a round o-ring. Thermostat has flat o-ring. What is round one for?

 

I thought the flat metal looking one was for the water pump. The round rubber one for the T-stat. Pulling from memory based on such little info. Hopefully you got 'em by now.

Might also be cam or crankshaft oil seals. Good on you if you did those as well.