A suspension trainer is a piece of kit that I think all martial artists should have. It effectively allows you to have an entire gym in your kit bag and it’s the only bit of kit I’ve used that comes close to the effects of weight lifting. Your bodyweight provides the resistance and you can quickly alter the length of the straps depending upon which exercise you want to do. A high-quality brand can be expensive, but you can get fully functional cheaper versions that will do the job just fine. A very versatile piece of kit that can be used in innumerable ways.
All the best,