this is what I do (as posted in another thread) and I'm beginning to do some lipidomics to figure out what is in the grease I'm using:

We actually save all of our used cooking oil/meat fat from our cast iron pan (olive oil and sunflower oil usually) and use that to lubricate our chains. When I ride behind my gf and she mashes, I can still smell the goodness.

Two bad points about this plan:

1. I park the bike outside my office at the uni and we have rabbit infestation problem at night. Unfortunately, the rabbits like the smell as well, and I often get rabbit hair (hare hair ... lol) in my drivetrain.
2. Often, when we run into the store for groceries or such, dogs like the lick the drivetrain. However, their owners don't like that and often try to pull the dogs away, which usually results in them urinating on the drivetrain.

So, if you can deal dog urine and hare hair, it's not a bad to recycle your used kitchen fat.