Block ice lasts longer. You may have an employer or friend who will give you freezer space to make your own block ice.
Safeway used to carry block ice but you had to ask for it at some stores (kept in the back).
Make a cold box around a large size cooler with 2 inch foamular insulation or soft insulation like blankets, extra coats, etc.
You could sew a cover for the cooler leaving enough space to stuff the batting in between. Use 4 pillowcases: stuff full and sew them together at the ends. Place around large cooler. Place large folded up quilt on top.
Use sealed packets of condiments commonly stored in the fridge. These are available online at walmart. Frees up space for other stuff in your cooler.
When I used an ice chest, I ate out of the cooler for 3 to 4 days, then I ate preserved, canned, or dry foods for 3 days, then got a day off for shopping.
-crofter