Should I get a rotomolded or injection-molded cooler for occasional use?

Get the injection-molded cooler. Rotomolded coolers are overkill for occasional tailgates or beach trips — they cost $200–$500, weigh a ton, and keep ice for days when you only need 24 hours. A good injection-molded one like a Coleman Xtreme costs $50–$100, holds ice for a solid day, and won’t break your back. The only downside is lower durability, but for occasional use, that risk is low.