How to keep salad fresh?

I love salad vegetables (lettuce, tomatoes.. anything that that you can put into a salad) but I don't buy salad ingredients often. I live in the middle of nowhere, literally (out my front window is a forest. Out the back window is a mountain).

I eat for one. When I buy salad ingredients they go off before I can eat all of them. They last 3 days then I have to throw them out. So I have no salad ingredients for the rest of the week. As a result, I usually don't bother.

• Is there a way to store salad ingredients to make them last longer?
• I'm thinking of getting mason jars, would that work?
• What's the difference between mason, Kilner and regular glass jars in terms of preserving vegetables, do they all work the same?
• Is there a better way to stop my spinach going flaccid before I eat it?