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Of course classes/instructors would be best, but without resources like those, what's the best way I can get started?
For example, are there any resources or training guides that can teach how to kick or any other stand-up fighting techniques that I can practice on a punching bag before I actually join a class?
Most attempts to learn martial arts outside of classes, without instructors, without sparring partners, lead only to ingraining bad habits. Don't waste your time trying to learn technique.
Instead, focus on becoming the strongest, most flexible, fastest, most agile athlete you can be. Then, when martial arts instruction is available, you'll be ready to take advantage of it.
Learning martial arts alone involves a lot of re-discovering the wheel. You will be a hundred times better off finding anyone who has a solid grasp of the basics to show you and train with you - whether that's an official school or someone you meet online who is looking for a training partner. That's because not only is there the movement of the technique, there's the range, the timing, and more which you really only get when you're working with another live human being who is responding as well.
Also, seconding Dave's recommendation for general fitness, if there is a particular style you are looking into, you can see what kinds of conditioning they do in terms of exercises that might be feasible for you to train on your own (I'm thinking calisthenics, push up variants, squats, etc. not punching logs or anything.)
