On reverse car salesman - use this on the company you know for sure you want. Likely the company you know for sure you want will remain that company even within a 10k range price difference (speaking to software engineers here). That being said, you can start throwing all sorts of weird shit on the table, if you've already negotiated your salary up. PTO is usually the first thing that comes to mind, but I've also seen "guaranteed right to wear flip flops in the office, forever, no matter what office dress code becomes" put in a very picky qa engineer's contract (which is funny because he showed up to his onsite in a suit and tie... And I haven't seen him in anything but flip flops since). There's a hardware laboratory here so I got "access to laboratory" put in my contract, and since then I've learned to solder by just hanging around in there. Remote work stuff comes to mind, maybe some sort of time-bound access to powerful servers, just see what you can think of.

Reason being, if the company has to give just one more thing to nab you, they'll feel like they really worked hard to secure the perfect candidate, there'll be no doubt in their mind, the recruiter/decision maker will always tell the story about how you were looking at other offers "but we finally secured her by putting the Foosball table right into her contract." And on the other side of it, you get that warm fuzzy feeling that you negotiated all there was to negotiate.