What functions/forms should all lisps have?

I'm writing a lisp and I'm curious if there's a consensus on what constitutes a "minimum lisp". I'm not planning to implement the full extent of Common Lisp, and probably not even Scheme, but I'd like mine to have all of the basics, whatever "the basics" are expected to be.

Any resources or suggestions on this? So far I've got car/cdr/cons, list, all the basic math operators, print, lambda, and/or/not, basic equality and numeric comparisons, eval, define, begin (block), cond, and if.