- shopping through the BA shopping portal is an easy way to keep Avios ticking over
- Avios credit cards (Amex etc.), though there are some chunky fees on some of them which means only worthwhile if really earning heavily & using 2-4-1 vouchers etc
- buy the odd case of wine through the BA wine club (Laithwaites)
- if you really don't want to spend money, sign up to something called "rewards for thoughts" - you get Avios for completing stupid market research surveys...the earning rate is pathetic (like, 25 Avios for a 20 minute survey...) but it's free to keep collecting and keep account active
just some suggestions