I've used and tweaked a few of the free workouts found here. It's worth checking out;
Rucking is a simple exercise: walking with weight on your back. It’s a low impact, full body exercise rooted in military training that is free and easy to start. You probably have everything you need to go through a rucking workout, and this guide will set you up for success. Rucking torches...
www.goruck.com
I stay pretty active year round, so for me, it's really about just getting the feet and joints /spine used to load bearing, as the GPP /fitness is there already. That's why I rotated in the above workouts with weight vest/loaded back pack and progressive loading. Seems to be working.
Beyond that, as far as my general fitness, it starts with hobbies

I mountain bike and dirt bike a lot year round. Still get to the MMA gym for kick boxing or grappling once a week. Point being I try to do things I enjoy as a means to keep in shape, as it keeps burnout low and the variation helps with general athleticism (which I've found is the first thing to decline in my 40's). I build and maintain a lot of MTB trails in my area too so lots of hiking carrying water, picks, sledges etc which helps. Anyway, I think it's important to have other athletics hobbies in the "off season".
Most of my structured workouts (I resistance train 2-3x a week) are built off the following template; multi joint BB lifts with a Wendler 5/3/1, 5x5, strong lifts etc base, then lots of calisthenics because I like pullups, dips, pushups, lunges, plyos, rings etc. I run once a week 2-3 miles but that's about it because I don't like running, but the movement pattern is important. If I miss a day on the mountain bike or moto, I'm on my concept 2 row machine for 30-45 minutes after the kids are in bed.