The big thing to me is the huge markup on options and accessories. Don't buy more than you absolutely have to from the dealership.
I bought a 2WD RCSB WT, only options being the locking diff and mud flaps (didn't even want the flaps but they were there).
I would have paid the $800 or so for the convenience package, but all the RCSBs around that had it were LTs or LTZs for $3-10k more with options I didn't want, and wouldn't pay for.
I would have even preferred the vinyl seats instead of cloth, but those were nowhere to be found. (If you're local and have vinyl and want cloth, PM me )
I paid just under $18k for mine, plus local taxes came to about $19,200 (employee pricing + incentives + $800 trade-in).
The other stuff that I do want, I'm adding myself for much less than getting them through GM. My wheels+tires were only $1200, plus I sold my factory ones for $600.. BedRug was $325 shipped on eBay (it's $490+tax at my local dealer). Doing a semi-DIY hard folding tonneau for about $300. Keyless entry and remote start is $200 installed at Best Buy (<$80 if you DIY, but I don't like messing with wiring).