Capacity numbers can fool you
A 45-quart cooler does not mean you should plan to pack 45 quarts of drinks and then somehow add ice. The cooling medium consumes a meaningful portion of the interior. Coleman recommends roughly a 2:1 ratio of ice to contents by volume for maximum performance in its hard-cooler use guidance, so serious ice-retention plans require more cooler volume than the cargo alone suggests.
Day trips and tailgates
For a few people and one day, portability is usually more valuable than expedition-level capacity. A smaller hard cooler or quality soft cooler is easier to carry, fits behind a seat and encourages you to bring only what you will use. If the cooler must travel far from the vehicle, handles, shoulder straps and loaded weight deserve as much attention as insulation claims.
Camping and multi-day use
Longer trips need room for food separation and more ice. A larger hard cooler can reduce how often you restock, but a fully loaded big cooler can become a two-person lift. For longer trips, consider separating frequently accessed drinks from food so the food cooler is opened less often.
Pre-chilling makes a real difference
Do not ask your trip ice to cool a hot cooler and room-temperature drinks before it starts preserving them. Coleman specifically recommends pre-chilling food, beverages and even the cooler interior. Keeping the cooler shaded also reduces heat load. Those habits cost almost nothing and can matter as much as chasing another marketing claim.
Features worth paying attention to
Good handles matter when the cooler is heavy. A drain is useful on larger hard coolers. Tie-down points matter in a truck or boat. Wheels can transform a large cooler on pavement but add bulk. Thick insulation can improve performance while reducing usable interior space for a given exterior size, so compare dimensions when vehicle storage is tight.
Bottom line
Size the cooler around the trip, not the biggest model you can store. Leave space for enough ice, pre-chill everything you can and think about how far you must carry the loaded cooler. The best cooler is still a bad purchase if it is too cumbersome to use.
Sources & further reading
Coleman: Cooler Use & Ice Guidance · Coleman: 45-Quart Example Specifications