I'm lacking a sparring partner, and there are no dojos where I live. I have no access to anyone with particular martial arts knowledge locally, and my equipment comes down to the floor, a bar, and a 50-pound punching bag.
My martial arts experiences include minimal Taekwondo training as a child (mostly forgotten), a green belt in Aikido (I believe that was 7th kyu in our school), and some street fighting techniques learned by sparring with a martial artist who trained at a local gym, but left after about six months. The style he taught was based on modified Wing Chun, and involved less finesse and more brutal methods, i.e. straight kicks to the side of the knee, going for the groin, shifting weight forwards constantly and aggressively to overwhelm the opponent, raking, attacking the throat and kidneys.
I'd like to know what I should train to keep my physical and mental potential as a martial artist as high as possible without a partner or a dojo. What sort of striking and kicking should I practice, what balance exercises should I do?
Currently, I use calisthenics for strength training and endurance training -- rope-jumping on bare feet, planking, knuckle push ups, jumping squats, pull ups, hanging leg raises and windscreen wipers -- and after training, I use yoga to stretch out my back and hips, by far the least flexible parts of my body. While a couple exercise pointers are appreciated, I'd like to focus on how I can train specifically to be physically formidable for striking and moving. Most martial art techniques are based on muscle memory, training your nervous system to optimize your movement, so yeah.