A question that begins simply, and move to complex areas quickly. Most preppers begin with a kitchen can opener, usually in pairs; with a P-38 on their keychain for backup.
This will get you in trouble, when you can no longer easily order replacements. The issue is two fold, first most kitchen can openers are pretty much at capacity opening can from the pantry, as it's what they're designed to do. Secondly, when opening gallon cans; the time to remove the lid is significant due to thicker metal, and poor leverage. I broke one and stripped the gearing on another myself, which is where this post comes from.
The solution is an industrial weight can opener with a lot of leverage:
I like this one, because the handle folds for storage and protection
The crank are is significantly longer:
Here it is with the handle in the working position. This helps because to get the long term storage rating, the lid must be over twice as thick as a pantry can! These are Difficult to open with a regular can opener, and that's how I broke mine earlier. But a problem corrected before the SHTF shuts down commerce, is no longer a problem.
This also is a recommendation that you eat some of the food Now, that you intend to live off of later. It would be really bad to open food when it means life or death, only to find you hate it, or can't eat it! It also gives the body time to get used to some of that food, in relative safety.
I tried another can opener that has some advantages:
This one allows the lid removal that avoid the sharp edges, and allow the can to be reused as a container. Unfortunately, it's not really up to fighting the gallon cans! It does a good job on the pantry cabs, and will see a lot of use; just not on the big cans.
I bought a can opener like a P-38, but the size of a cell phone; it will open the gallon cans, just very slowly! My hands would bleed if I tried to use the standard P-38, if it even survived!
We try to eat about half of our menu from long term storage food. We simply use half of what our budget is for food, to resupply the homestead, and gain stored food each time. Fortunately, we have found some really good items, and fixed some marginal items with better recipes. The last gallon can was buttermilk pancake mix, and it is exceptional taste, but the number of pancakes is underestimated by about half. Again it's information I needed to plan, so I'll need to buy more!
I believe Patriot Nurse had it right, when she recommended " beans, bullets, and Band-Aids" to all preppers!