In th ehot summer I still wear jeans, but I have a pair that's light colored and breathe really well. In the winter I just have a pair of normal blue wranglers.
As far as upper body, I will ride in anything. Tank tops, tee shirts, Camis, whatever. But keep in mind if you fall you cang et your arms scraped. I wear a light sweatshirt if at all possible, but in the summer I feel your pain so I wear a white athletic tank top. ALWAYS wear your boots...I have a pair of Ariat workboots that I LOVE to death and they breathe really well too