Co-op and Morrisons
If you shop at any of these, you can make your savings work harder by transferring some money to a supermarket card, then just spend it by shopping normally.
E.g. I know from my household records that I spent £xxx at Asda, £yyy at Tesco and £zzz at Morrisons last year, so I'll be buying cards that will take me about 12 months to get through, and then each month I'll be running the card balance down and my cash savings back up. (Cards don't expire provided you use them every so often - e.g. Asda expire after two years of inactivity, so I don't see that as a problem!)
For Asda (as I have it open at the moment) the way to maximize the bonus rate is to put exactly £280 on each card (so if you wanted to deposit £560, you'd use two savings cards. Depositing more than £280 on a single card doesn't earn you anything extra, and depositing less than £280 earns a lower % bonus rate, but is still worth doing if you don't want to fill a whole card.
You can register the cards (again, I'm looking at Asda - check the others) so if you lose one, you can recover the remaining balance. If Asda goes bust, you will be out of pocket (I think Tesco ring fence the cash)...
Looking at the last two years' spending records (we all keep household spending records, don't we?) I am confident that we'll get through at least £1k at Asda next year, so will happily transfer £1k from my savings account earning 1% to four Asda Christmas Saver Cards and earn around 5.35% in a shorter period, whilst replenishing the savings account each month with the cash that I didn't spend in the supermarket.
I'll do the same for the other supermarkets.
If you enjoy the "buy 6 get 25% off" wine offers that come around occasionally, then these savings cards can be used for those too