A little advice please on preserving excess canned tuna

I recently spoke to this "friend"(using the term in the most loosely possible way) of mine. She's one of those people who used to be chunky and has now lost weight(due to a dr's order) so she feels that everyone needs to lose weight and tries to push everyone into it(yet she give absolutely ZERO advice as to how to accomplish it and says nothing on how she did it).....Moving on, a few days ago I got into the line at the super-market and sure enough there she was right in front of me(I thought to myself...BWAHAHA now I've got you.) so I of course do the customary greetings and hug(While staring down and memorizing every item she purchased) she had: Various fruits(fresh not canned), Bunch of fresh veggies, a GIANT can of tuna(seriously you could feed an entire village for a week on this 1 can).
thats where I will end the list.

the Advice I need is how to preserve tuna. Obviously I cannot eat an entire can myself. So how can I preserve it to be able to buy such a big can and make it last after I open it?

Answer A:

Why not just buy smaller cans of tuna?

Answer B:

Tuna is a top-of-the-food-chain predator fish that's not considered very sustainable. It's pretty much not a farmable fish and the wild populations are under enormous strain from overfishing. Healthwise, being an apex predator there are concerns about bioaccumulation of toxic metals such as mercury in the flesh of tuna. If any of this concerns you, you might want to substitute a different fish into whatever fish-and-vegetables diet you are trying to recreate from this woman's shopping cart.

Answer C:

Canning tuna destroys a lot of the texture. You could probably freeze excess canned tuna in your freezer without much additional loss of texture or flavor.

Answer D:

What if she was shopping for someone else? I don't eat any animal products at all, but I often shop for other people in my family at the same time as I shop for myself. Which leads to shopping carts full of fruits, vegetables, whole grain products, and ... bacon. Or hot dogs. Trying to recreate my diet from my shopping cart would lead to some hilariously bad conclusions.

Reply to A: I was going for the Deal not the sustainability(end up saving like $7 for the same amount)
Reply to B: Most canned tuna is Albacore and is not yet threatened. while I admit that it is completely being over-fished.
Reply to C: Freezing does seem to be the key.
Reply to D: She lives alone and is currently dating a vegan chick, so I know the Tuna is gotta be for her.