Yesterday I was jamming with my drummer, and usually we have a bassist too, but not that time. I realized that if I just strum chords it sounds ok, but if I switch to any kind of leads that I usually play with the bassist, it begins to sound extremely empty. To avoid that I tried playing the root note on one of the last 3 strings, and play some sort of lead on the first 3 strings. Kinda tricky, but I think i'll get it if I practice on it. But maybe you know any other tricks? Also, are there any musicians that play as a duet of guitar+drums(except white stripes)? Maybe I can get some ideas from them too.

It might not be your kind of music, but listen if you care about yourself. Never does it sound empty.

There you go. That's improvised more or less. Handle the bass, and outline the harmony in your solos.
Don't tell me what can not be done

Don't tell me what can be done, either.

I love you all no matter what.
Take a look at The Black Keys, its a Guitar and Drum duo. I learned a bunch from them, on how to play without a bassist.
I play guitar.