DH and I have been TV-free for most of our adult lives, so ten years or more. Every time we've tried tentatively reintroducing television, we've had to admit after a short time that it was a negative influence in our life, and that the quality of our relationships and the quality of our leisure time was deteriorating. For us, no-TV is the default setting.
We do watch the occasional rented movie on the computer, maybe like once a month, without the kids, but that's it.
My kids are still little. These are things they do, things DH and I do, and things we all do together. We have a very tiny budget, so we only rarely drive anywhere more than a few miles away, or eat out, or anything like that.
linger over meals and talk
listen to music and dance
run around outside
playing with toys, inside and outside
playing pretend games
visit with family, friends, neighbors
visit the (free) nature center at a local park
visit our CSA farm
visit a local historical farm, also free
throw rocks in the river
play in the creek
hang out at the library, especially when they have free programs
go for long neighborhood walks, with a bag to collect "treasures"
make blanket tents in the living room and play camping
build block cities and then knock them down
play board games
play kiddie basketball, indoors in the winter
go to the bookstore and read all their books and don't buy anything
pack a lunch and go eat it in the food court at the mall, and then window shop
write stories and poems, make books
play wrestling, tickling, and tackle games with Daddy
play with the cats
go garage sale-hopping, or thrift-shop combing, or curbside trash-picking
make ice cream, yogurt, italian ice, or yummy baked stuff
roll and cut out cookies
make paper dolls
jump on the bed
"adult" activities, ahem...
(lots more time for that without TV, provided your kids will go to bed without too much trouble!
Gosh, I could go on and on and on, but this is getting long.
I would really encourage you to take the plunge and try it. Just do it. Don't dwell on what you're missing. Use the opportunity to try out all kinds of stuff you normally wouldn't do, and see what happens. If it's not working, you can always go back, but you'll never know how it will be if you don't try.