Consider looking into Crossfit! (I can feel the thumbs down that are coming my way, haha)
Some of the outdoor activities that people do with Crossfit (flipping tires, carrying objects, jumping over natural hurdles, throwing self-made sandbags of various weights and sizes, just to name a few) could definitely good activities to add in if you get the opportunity and your clients are not contraindicated for those activities. I was dubious about the whole Crossfit thing at first, and some things are still pretty “out there” to me, but I’ve used the above exercises quite effectively in my clients’ routines as welcome changes in their programs every so often.
You might be surprised what you can find in a public park/public area that can present a welcome and surprisingly safe challenge when you’re cautious. Use your imagination. That’s what’s going to set you apart from other trainers!
Also, you might consider investing in some orange cones to set up some agility drills, some jump ropes, a rope ladder, etc?