I have a pair of Wald folding baskets on my rear rack that I just open on of them, throw my backpack in and then cover it with some bungee netting. Then when I get to work, I pull out the bag, fold the basket and I'm good to go. I keep wanting to get some Ortliebs, but the wald baskets just won't die (they do creak occasionally), so I have a hard time justifying the expense. The waterproofing of the Ortliebs would be nice, and sometimes I wish I didn't always have the racks always on there, but I rarely ride in the rain (especially not when commuting except on the way home when a storm comes up unexpectedly), and having baskets there and ready to go is nice when I decide to make an unplanned last minute run to the store for dinner supplies on the way home.

Baskets can slide way back on my rack to get out of my heel zone and are nice because you can just throw whatever bag you have in them and go.