The top is rounded on the outside so nothing will fit on top. The top on the inside has a bunch of room that helps with capacity.This 21L size is not bad for short trips, vacs etc. After using this I think 35-42L is the perfect size for me after using the 53L which was maybe a bit big.Works very well and the temp is very consistent. Keeps things either cool or frozen if that is what you want. Easy to clean and light weight.