Should I buy a cooler with a built-in ruler?

Skip it. Built-in rulers are gimmicks—awkward to use with a fish, and they scratch or fade fast. A separate $10–$20 aluminum or plastic ruler works better and clips to your belt or goes in your tackle box. Only consider a built-in ruler if the cooler itself is perfect and the ruler is a minor bonus; don’t choose a cooler based on it. Spend on ice retention instead.