DH and I have a half acre field about 3 miles away from home.
We keep chickens and ducks there, so I am usually there twice a day anyway.
We changed our mortgage to buy it, it cost £8,000, which we have been told was very overpriced, but we know the farmer well enough to know we wouldn't have got it cheaper. The area it's I means we will almost certainly never get planning permission.
In the summer, we have parties there and we camp. We have a couple of sheds up, one is a bunk room with a bunk bed and camp bed in it. The other has a camping stove in it and chairs. We keep mugs, plates, knives, forks etc up there (mostly provided by freecycle)
We have plans to put a small woodburning stove in the kitchen shed, and more permanent seating that will double as beds, and a fold down table.
For parties, we put up lights powered by a small generator. We have a brazier so we can keep warm as the night turns chilly, and he dc roast marshmallows.
DH and his father built an earth loo a couple of years ago, but up until then we had a camping loo in a tent. The earth loo is fantastic - occasionally needs levelling, but it doesn't smell at all, and saves us having to hire a loo when we have a bigger party.
Practicalities that I can think of are general maintenance, keeping the grass cut (DH is an ex mechanic and has done up a garden tractor that cost £20 - the dc tend to see cutting the grass as a treat), fencing/walling needs to be checked regularly and fixed as soon as there's a problem. We have dogs, so we make sure the fences have no gaps in them.
We have public liability insurance to cover us in case someone goes in and hurts themselves. We had to change to NFU Mutual for that, but it actually ended up cheaper than our previous policy, even including the field'a cover.
Freecycle has been amazing for us. We've got cups, plates, pots pans etc, and also have a swing and climbing frame for the dc
We have some rigid rules for the dc, and visiting dc, like no chasing chickens, no climbing on walls (dry stone walls, so not safe for climbing on).
Sorry, that's quite long! Having our field is, without a doubt, one of the best things we've done. If you have the opportunity to do it, it's well worth it!