Shirts that toe the line between conshirt and something you can wear around in public, buttons, sketches, quick badges that amuse me.

Hello. Different people like different stuff, but I can tell you what I buy. (Though, come to think of it, you might be better off asking artists what they sell. But anyway!)

I like to pick up prints, and sometimes pre-done sketches -- almost always PG-rated. Stuff I could put up on my walls without fear, basically! Different types -- sometimes cartoony/humorous stuff because it amused me; sometimes gorgeous, intricate pieces because they're so technically impressive; sometimes more stylised pieces. Whatever catches my eye. (Obviously a lot of adult art gets sold at cons too, but wanted to let you know that there _is_ a market for non-adult stuff.)

I don't often buy T-shirts at cons, I gotta admit. (I have too many already...) I'd be more inclined to go for shirts that have cute, furry things but aren't overtly Furry and which I could wear around. (I didn't get this at a con, but here's an example: https://shirt.woot.com/offers/nyans-dream ) But to me as an ignorant non-artist, selling T-shirts sounds tough -- you've got to pay to have them printed in advance, stock up in a range of sizes, etc. I know people like getting physical swag at cons, but if it's your first time maybe start with a Cafepress/print-on-demand thing? (Like, have a couple of demo-model shirts that are not for sale, maybe wear one yourself, and make it really easy for people to order one right away, maybe at the table?) But, again, don't trust me on this! Talk to real artists who've done con dens before.

Lots of people want to get con badges, especially early in the con, and commissioned sketches in general. Art done at the con. Definitely get set up for that! Clear price list, system for keeping track of who asked for what as well as their contact details and how much they paid, all that jazz. If I don't know an artist and am wondering whether to buy a sketch-commission, I'll judge them by the pre-done prints/sketches they have on sale, so that's another reason to have those.

I sometimes get random little knick-knacks, especially if they're appropriate to the con theme. (Pins/buttons/badges, accessories like a wristband, key rings, what-have-you.)

Good luck!

I like pins myself! Pins and badges.

As far as shirts goes? Species-specific. I would be pretty inclined to buy a rooshirt. What else would be as appealing to a furry?

I mostly just buy art but wearables are a good thing to sell and it is something I might buy.

Adding on to the shirt idea, well I like eagles and I can never have enough eagle shirts.

id say anything related to the theme

I like pins, charms, and buttons myself! :3

I tend to go for plushies and stuff, other odds and ends. I'm a bit niche with tshirts, but I do know a lot of friends go for shirts that are subtle furry. Maybe animals or nods to shows or fandoms, but not HEY LOOK AT ME IM A FURRY YIFF YIFF or anything.

I haven't been to a con before, But I'm pretty sure I would be down to get anything from an artist I loved.
Probably shirts, cups, pins and charms

I love buttons and stickers, since they're a pretty inexpensive souvenir and I love putting them on my bag or fursuit tote. I'll occasionally spring for a PG print if it's something I really like, and I like small, generic originals like ATCs a lot. I feel like at-con art is pretty popular too.

I don't mind overtly "furry" shirts, as long as they're not suggestive at all -- frankly, I don't want to wear that sort of stuff out in public, and don't want to spend money on shirts that I can't wear 95% of the time. Ones with cute/cool animals on them are my favorite!