It's practically guaranteed, and many people rate it higher than a hot chocolate on a cold winter night.
I will acknowledge your support in a commit message to the SBCL Git repository.
Suggest a subject for a blog-post. I will collate all suggestions and you get to vote on them. I will write on at least top 5 subjects before the year is out. I will also send you a small personal surprise gift. Emphasis on the word "small". (Incl. previous perks.)
In addition to previous perks, I will call you on Skype, and we'll talk about whatever you like for the next 15 minutes at minimum. Consider this a golden opportunity to nag me about your favorite SBCL bug or feature request.
In addition to previous perks, you can make a wish, and I will do my best to fulfill it. Obviously, there are constraints. Most importantly, if it is clearly going to take longer than an hour, I reserve the right to veto it and ask for an easier wish. ...but you may be surprised by how much I can get done in an hour, as long as it's not Monday morning.