Along with the size and space constraint, durability is one thing that you need to consider. This is very important whether you plan to use it frequently or not. Reputed brands also give buyers a warranty or guarantee, so the steep prices are worth it in the long run. Insulation is the second most important thing. Next, make sure it is portable and has a separate space for cans and bottles if you plan on carrying those too. Different bags for bottles/cans are also available.