I sometimes wear neoprene boots for swamp-hunting. I have even walked ~8km on dry land in 100-degree heat here in Australia's Top End on one occasion, and was surprised at the fact that my feet didn't cook right off! The soles held up perfectly!

Just throw a pair in your day-pack.

Mine are Mirage TTZ, and when shopping for them I noticed a huge variation in quality among brands. If you go this route, buy the best you can afford.

BTW, Mirage also make a neoprene 'workboot' and a 'rock-hopper all-terrain' model. Might also be retailed under the Mares brand-name in some countries. Check 'em out here