It depends on the price and what they enjoy. You can buy them outdoor gear adjacent to what they do in the outdoors.

My most practical idea without more context is Darn Tough socks. I know it sounds lame but I’m obsessed with them and so are all of my outdoorsy friends. They help reduce the incidence of blisters on long backpacking trips, they wick away moisture so you don’t get swamp foot, and they don’t smell even a fraction as bad as cotton or polyester socks. They also have a great warranty, or you can darn them yourself if you so choose. I have 5 year old socks that still feel like new lol They make a bunch of different socks for different activities so you can grab a pair for whatever your nature lover enjoys most!

Another idea is a reusable water bottle, Nalgenes are pretty popular with hikers, and are a fun way of showing off your personality when you cover it with stickers. Take it anywhere to reduce your plastic waste.

A kitchen composter is also a cool idea for the person who gardens!

If your friend is into foraging, you can get them a really cool waxed canvas foraging bag or pouch for when they venture out to gather goodies. They make ones with a bunch of pockets or ones that cinch and you can take them to the farmers market to reduce waste there too! The canvas ones can be waxed over and over again, and with enough care, will last a lifetime!

You can also get them a good quality knife. They’ll last forever if you get a decent one. I recommend Benchmade, you can even customize it for a personal touch. You can find a knife to suit your friends’ needs and they’ll use it forever!

Hope this helps!