For me it's not the weight of carrying a second pair of shoes, it's the space they take up. I'm planning a long trip now and have decided to switch to clips and straps instead of clipless pedals, which I've been riding for about six years now. If you only want a spare pair of shoes for walking to the restaurant from your motel, then probably any pair of light, compact camp shoes will work. I plan on doing some hiking and camping on this trip as well as cycling though, so I wanted shoes that could handle that, like some trail runners or light hikers. Once I began considering shoes like that, it didn't make sense to bring them in addition to cycling shoes.

I had been using Mavic Alpine shoes in my quest to find a walkable cycling shoe. These are pretty good, but as always, the more you get to the middle of the good for walking/good for cycling continuum, the worse they get at both things. For my short tours (ten days or less) around Japan, these shoes have been fine.

I have been using MKS Urban Platforms with clips and straps and they've been great. I mostly wear Nike Pre Montreal Racers with them. They have a really soft sole, so I'd be concerned about wearing them with a cage pedal, but they feel great on the MKS Urban Platforms. One other benefit of something like the Urban Platforms over cages is that you are more able to yank your foot out the back with straps tightened should you need to in an emergency.