I get stuff out my girlfriends and she does the same it’s no big deal.

Ummm no

i only look at my mum’s cupboard and tell her she’d survive a year without food shopping.

Not to be nosey but I help myself at my friends house

Tell them that you have it all stored in the cupboards at their place and if you run out of food you will come over and get it.

You obviously live in a built up area that has a grocery store on every block. That's cool when everything is going smoothly. What happens if you & partner both lose your jobs, suddenly there's no money? What if the power went out for a week? What a natural disaster happened & cut all the trucks off from getting into the city? It's smart & more cash efficient to stock your cupboards. She's just trying to clue you in but obviously no clues getting through here. Stay petulant young one.

My family (My parents, my brother, myself) all have a good stock pile of canned food.
My dad is very concerned about what happens if the power goes out for a long period of time, or some natural disaster happens. Not like the apocalypse/doomsday peppers, but he always keeps enough to last probably a month if anything happened. So my brother and myself are the same.

How old are your in-laws? People who have had to live without (for example anyone who lived through the Great Depression) stock up on stuff like that. Both my grandparents did.

It also makes sense, so if there is a disaster of some kind the supermarket shelves will he stripped bare in a flash. Keeping a stock of non perishable items makes sense and it’s smart .