My own kids are just past this age (one still in upper primary, other teen) but with a neurodiverse family and no family nearby we always had to plan well.
I always brainstormed with the kids what they wanted to do during the holiday:
-things outside of the house that were free and cost (with the realization that certain things are too expensive to do).
-what they would like to do at home if it's good weather vs bad weather.
-what they would like to do one-to-one with me (at home)
-books/films they want to see
-favourite meals
We'd try and make a schedule first for the week for home vs out days or split days (we'd usually get out in the morning on home days if it was dry as a whole day out was often too much for them).
Because one of mine is AuDHD I made sure to plan in one-to-one activities with each of them at some point during a weekend/every few days and safe activities with the other one to do with less supervision.
I sometimes bribe my kids with activities like reading (e.g. favorite snacks or they get to pick dinner).
Walks - playground hopping (we could spend the whole day walking or cycling round our city), taking our pick from local woods/canals/fens/parks/river/nature or botanical garden, or combining with a city walk - lots of free resources online to make our own guided walk. We take binoculars/bird book or if heading to park football/frisbee. All of this is free (if we walk cycle there) or minimal petrol cost. Always take your own flask of tea/coffee and lunch/snacks with you.
Free museums (in the UK I guess this is more! No museums are free in the country I live in). Travel would be the cost here. We would always take our own food and drink from home.
Train travel is quite cheap for young kids where I live so exploring another city is an option (but need to plan ahead).
Library.
Look up events in nearest town. Often there are free festivals/performances/lunchtime concerts. In the last month there's been a music festival in my city (mini free 30 minute concerts both weekend days) and. a fantasy festival with lots of kid friendly interactive activities around the town.
We have some cinema vouchers knocking around so am waiting to see what to take them to this summer. I will buy snacks at home to save money (I don't eat at cinema anyway). Cost - parking unless we cycle!
Board game/cards afternoon. If it's sunny we set up in the garden, lots of drinks and snacks to keep us going.
Cooking/baking - this is the type of thing It's hard to do with both my kids at the same time, so we negotiate what activities they can do by themselves.
Downtime - TV or gaming or reading...anythign that doesn't involve a lot of input from me!
Music practice.
Arts and crafts - sometimes this is organized/structures, sometimes I just plonk a lot of stuff on the tabel and let them crack on. My oldest DS loves digital art but is also making a dragon hand puppet out of cardboard atm.