Contraptions
I never thought much of the various gimmicks and tennis devices I've seen. Most fade away. Stick with good rackets, shoes, tennis balls, and modern clothing that breathes and blocks sun.
You can do most of your training with a wall or a ball machine when you can't get a partner.
A ball basket is probably the best tool among all the other essentials of tennis. You can do self feeds or drop and hit shots as well as just taking lots of serves.
