Wicking polo shirts are sold everywhere now. The Dollar Stores have them for around $10 or you can get real good ones for 3x that. Those are all I wear anymore because I sweat like a pig year-round.
MTB shorts are good for riding but not good for not riding. They smother my groin area.
If I'm not riding all day I just wear shorts/pants and regular undies.
I don't ever wear "biking" kit. Even on organized rides. Looks too dorky.