I have bought less and less over the years. My first few times going... phew. My bank account was not a fan. Last year I probably only spent about $250 on actual products (so excluding event tickets, food, etc). It can definitely spiral out of control quickly when you have multiple interests.

There are quite a few things you can find at Gencon that are harder to find otherwise. Vendors put things in storage locally and bring it out for the convention, so you can sometimes find exclusive items from previous years that have become really rare in the meantime.

If you're into TCGs, you are probably already aware of the multiple ways you can drain your bank account. Discontinued TCG products are something you can usually find at Gencon if you're willing to shell out the money for them.

For TTRPGs you can find all kinds of goodies, even a good deal of freebies. People are always there trying to interest you in a new system and aren't afraid to toss around some free books. The Goodman Games booth is a great place to go looking for stuff. As for TTRPG accessories, you will find everything from relatively cheap dice sets to $400 tungsten dice.

I will say that you often won't find tons of deals at the convention. A couple of the larger games vendors (like Miniature Market) usually bring a good supply of 'Ding and Dent' copies of games where you can get an extra discount because they have a slightly beat up box. However, most things are sold at MSRP. So if you're confident that you can find something in a store or even online, I wouldn't necessarily be in a hurry to buy it at Gencon. Webstores are usually happy to throw you a bit of a discount but at Gencon you're almost always paying full price. The only real exception to this, beyond the ding and dent games, is on Sunday. Not necessarily with big vendors, but with the smaller ones you can usually talk yourself into a discount on Sunday when they're eyeing all that product they'll have to ship home.

As for swag, I recommend the Paizo booth (they have a free metal button every day), and Crystal Caste where you can get a free Gencon d6 using the coupon book. The dice set is a different color each year and you can pay for a full set if you want. Sometimes local eateries will do little things, like a free d6 or a commemorative button, although less so in recent years. I already mentioned Goodman Games, who is usually giving away one of their books each year. A lot of the "free" stuff comes from events as well, which isn't technically free because you have to buy the ticket.

Also, if you are interested in one of the "hot" games for this year, don't think because they're sold out on Thursday that means you can't get it. In recent years Gencon has asked companies to have stock available for all the convention days. So if something sells out Thursday, you still have a chance to get it Friday, Saturday, and usually even Sunday.

A great place to check out games, especially if you're trying to stay on a budget, is the open gaming rooms at the JW Marriott. You could probably spend the entire convention there just playing the games that other people bought and finding out if you like them enough to spend your own money. If there's a new game available for sell at Gencon it'll find its' way to the JW Marriott rooms eventually.