Finding Alternative Uses For Existing Products

I just noticed a new search string that brought someone here:

slash fiction substitute lube

Not sure what you're looking for, exactly.
Are you looking for an existing piece of Slash fiction that prominently features some sort of substitute for standard lubrication (AstroGlide, KY, Vaseline, etc.), or are you looking for ideas for a piece of Slash fiction that you're writing?
If it's the former, I can't help you - Slash fiction just isn't my bag. I mean, if you were talking comics, and you said something like, "You know, the story when Mr. Mxyzptlk traps Superman in this sort of demented version of MTV," I'd be able to help you out. Not so much with the Slash fiction.
However, if it's the latter, I can offer a few suggestions, though you might want to check with your doctor to make sure they're safe to use.
Obvious choices are things like Crisco or, cooking spary, or vegetable oil, or, if it's some kind of Food Network Slash, you might go with EVOO (Extra Virgin Olive Oil). If nothing is on hand, you can always go with good old-fashioned spit. Hand lotion would work, I'm sure. If being kosher isn't an issue, you can try bacon fat. Last Tango in Paris showed us an effective use for butter (though I'm sure Brando would have rather just stuck with eating it rather than using it for sex). If you're in a gargae, you could try motor oil, or WD-40.
In any case, there is a vast panoply of materials with low-viscosity that could meet your Slash fiction needs. My best suggestion is to just try things out - whether in real life or your fiction - and find what works best for you.