Self bondage is out there. BUT it is best to learn from some one who knows how to do it to some extent. You can go to conventions and such and watch then go home on your own and try it (as long as you follow safety procedures). i do self bondage to practice and have a good time on my own or when my Tops are busy with their other play partners.
One suggestion on solo things anyway. Self bondage is good for learning to tie and finding out what it feels like tied. so ya get the best of both sides so to speak.
you could try wax play on yourself, altho it wouldnt be the same if you had a partner,, but you could still learn the basics of it and do it on yourself.
All the stuff i can think of is basically different forms of play. Learning to use a flogger, and other things of impact play, ectect. They're not really at a deeper level as i like to think of it of D/s. They're what's used in scenes and what not, but it's not submitting or Dom-ing anyone because you are by yourself. So you would be learning the tools of the trade not necessarily the emotional/mental core of it.
good luck, eventually when you're ready you'll find someone, and i figure if you do learn some of these things that interest you on your own you'll be a step ahead of a few others out there.
~j~