Some dealers have a package of extras they include at the show. Beyond that, the WDH is the most common item for a throw-in. Beyond that, you try for specific items, or just ask for XX $'s of store credit to buy what you want at the dealer's store.
Shows are a good time to find deals, but the "show price" isn't usually the absolute lowest price. Typically they leave some room for trade-ins, so if you have a clean deal, you should be able to get a lower price.
And if you negotiate a little and then walk away "to think about it" my experience has been that dealers are very aggressive in after-show follow-up. If they fill out a sales lead sheet and have your number, you'll get a call after the show. On one unit we considered, the salesman called 2 days after the show and the first thing he said was they would drop the price another $1,500 from what had been their absolute lowest price 2 days earlier at the show.
2005 F-150 FX4
2013 Rockwood Roo 23 IKSS