The new setup looks nice! Not just losing the trailer, but the new bike as well!

Your new situation looks a lot like mine, with two full panniers on the back. On my school/work days, I'll have all my books in one, and the other will have work clothes, change of clothes and shoes (I have clipless pedals--don't wanna be clopping around in those shoes all day!), a couple of meals, toolkit, bike lock(s), and whatever else I think I might need.

I think it really just comes down to packing your bags efficiently. I have to keep everything very organized, or else it won't fit.