https://www.nielseniq-onlinereg.com/?cpid=1C06C1DE0C&fbclid=PAAab20auBSiObbRXufPWwgiUbEa1gP8Wr51R5UXkpDQ6HqDh56a3Sin11IjwaemmthATlKqq8Yw6LrNWrTTtCfP4jUGjHyj4JRXfu49U3fKNi0zdUYrHoMQxzJsOZtVrJUnqzBOpjX-Vsej8oWRupNSQyy
This is the Nielsen Shopping Panel.
I've been on it for approx a year now, and have accrued points worth over £100 to use on a wide range of gift cards (or a prepaid digital Mastercard). I downloaded an app onto my phone, and every week I upload my food shop receipt and scan each item. You get bonus points for maintaining 4-week and 12-week streaks, and occasional surveys earn you another handy bonus.
Definitely a long term thing, but it doesn't take me ages as I do a main shop/scan it all at once, and could be very handy for Christmas etc.