I'm sure they're okay if you only give them occasionally. Ally has about quarter of a tin once a week. You can get reduced salt ones here but I don't tend to look around shops for them, if I can see reduced salt ones, I get them tho.
For the potato I get a jacket potato, scoop out the white stuff, grate some cheese over it and throw some peas over. It's not as messy as it sounds lol.