How can I make my own chamois cream?
Most of your chamois creams/"butt butters", such as Paceline's "Chamois Butt`r", are fairly conventional combos of standard skin cream ingredients, with a heavy emphasis on lanolin.

I've never tried petrolatum (though many swear by it), and I'm a bit skeptical as to how it would fare compared to the more skin-cream-like concoctions.  Plus it would make more of a mess of the chamois and be harder to launder out.

I'll admit that the commercial concoctions are a bit expensive, but a little goes a long way, so it's not that big of an investment.