My typical European beach holiday gear is 5D2 & 50/1.4
I'm tempted to pick up a wider prime though somethign like the 28/1.8 & use that on the 450D to travel even lighter.
pancake or 35mmF2 + 6D
I'm still waiting for the pancake F2. That's probably the one lens that I would replace the 50L with.

It's a real interesting subject and hope you get a lot more thoughtful replies. 
