I don't know how limited your space is, but I'd keep an eye on wherever you ride to make sure your pasture condition isn't deteriorating.
You can put up cones (like those orange safety cones) and use them as markers for circles, serpentines, figure eights, leg yields. I guess you could probably do the same with tiny flags or metal t-posts (maybe somewhat less safe, though). Oh, and use them for markers for gait transitions (e.g. we're going to trot at that cone, canter there, etc.). You don't have to have a circular arena to do any of that -- if you land is really long and narrow, it may just mean that your circles are smaller, or figure eights are squished, or whatever.
You could use the cones to demarcate where you might put a round pen in the future and ride there. My last barn had an "outdoor" arena that was a dirt arena with no fence around it. The lack of fence was really challenging, in a good way. You had to really work to keep your horse in there without that barrier. It was hard, but it led to me having a lot more control over my horses. You never really realize how much you lean on having that arena fence until you do it this way!