What is the most important feature to look for in a cooler for a week-long road trip?

Thick insulation is the single most important feature. Look for 2–3 inches of foam in a rotomolded cooler (like Yeti or RTIC) — cheaper thin-walled coolers lose ice in two days. Hard latches and a rubber gasket seal also matter, but skip built-in cup holders or bottle openers. A 50–70 quart size works for two people for a week.