Just as the title says really. I've read a few threads where people either mention a fortune doing a top-up shop or mention doing a top-up shop as a job that needs doing in the week.
We shop once a week and buy enough food for the week. We then don't buy any more food until the following week. Other than folks who have very little storage (or possibly very large families?) I can't really understand the need to do a top-up shop. I mean obviously if you want to go and get something different to what you have in, that's fine. But why do it if you see it as a chore?