A bunch of fancy-schmancy hiking/camping gear. Why do I need an ultralightweight tent or a really cool hammock when I haven't backpacked in years? Good question. While we do hike, and do plan to camp this year, we have a 4 and a 5 year old, and my husband is iffy on camping anyway. 3 miles is the kid's max hike, and they definitely won't be backpacking. We'll car camp, and so all we need is basic gear we already have. I don't need a backpacking stove because we have a propane camp stove, and I don't need a spendy water purifier because we'll be able to bring in plenty of water for drinking and cooking.
I think a lot of it is just aspirational. If I owned the nifty stuff I'd get out and use it - but I know that isn't really the case.
I love backpacking. You don't need most of the expensive gear do to it. In fact, you're better off going minimalist - a lot of the gear that gets advertised isn't very useful and just weighs you down. Lightweight gear is good, less gear is even better.
You need a good shelter - I prefer an ultralight tarp, but will take an ultralight tent if bugs are expected. And you need a sleeping pad and sleeping bag, a set of lightweight clothes (pretty much anything but cotton), backpack, something to treat water, a stove (if you want hot food and cannot make campfires), food, and a few odds and ends. The backpack, tent, sleeping bag and pad can usually be rented if you don't already have these. You probably already have suitable clothes. For water you don't need an expensive/heavy filter, just use
Aquamira which is cheap, super light, and doesn't leave a bad taste. It's very easy to make a homemade alcohol stove, which is also very light (an online search provides links to many tutorials).
My wife doesn't like backpacking so I go on short trips by myself or with friends.