Don't get a pet, even small ones can be expensive and if you can't afford the vet and opt to have the animal pts that's another £100 and a lot of guilt
We pick up board games from charity shops and have a gaming afternoon. We have 2 teens and an upper primary aged dc and everyone enjoys playing. Occasionally I'll buy a cheap new game for the switch that we can play as a family. I am useless at all of them and the dc tease me. We might make some popcorn to eat while we play
We all read. I find Vinted good for books, better than Amazon a lot of the time
Tesco vouchers help a lot. I pay for everything with my credit card and pay it off the next day to build up points quickly
Look to see if you get an extras with the companies you're with. Sky give 2 cinema tickets per month. If you buy insurance for just a couple of pounds then Compare the Market give you 2-4-1 cinema tickets. For a while Octopus were giving away free child's tickets, they now have an offer on adult ones. They also provide me with a free coffee each week. We get free Disney+ with the Lloyds.
We might make some pizza and watch a film together. If I'm organised I'll get Krispy Kreme doughnuts the night before using the Too Good To Go app, so we get 6 for £4.65 (still overpriced but dc love them and so much cheaper than full price) and you get points towards free ones
Going for walks
Seeing friends, either for a walk or just inviting them over for tea and homemade cake
We sometimes set dc a challenge like learning to juggle which can be fun
Oldest one likes crafts and jigsaws.
Book early. There are some family rooms available at Travelodge for £35 during Easter school holidays. Book one and do the free stuff that local to it but new to you. If you travel by train get a Railcard with your Tesco points
Planet Offers is good depending on where you live for some good discounts. Reminds me of how Groupon uses to be when it started out