You can buy a lot of stuff at Kumoricon by going to the Dealer's Hall and Artist Alley. What you typically would find in a dealer's hall would include: Figurines, cosplay (Not all the time), mangas, t-shirts/bags, plushies, and pretty much anything along those lines.
For the Artist Alley, it's pretty self explanatory. You basically buy art from artists in the local area or other places. They typically sell buttons, keychains, posters, art books and so on.
Typically, from my experience, an average congoer normally brings around 100-500$ possibly. Why? Because items in the Dealer's Hall and Artist Alley are quite pricey. And if this is your first time, newcomers have a tendency to want to buy EVERYTHING, mainly from excitement and all. Now, I'm not saying everyone brings that much money because a majority of the congoers also set themselves a budget on how much they spend and on what.
For me, I typically bring 70$. 50$ for con stuff and 20$ for food mostly because I live like 10-15mins away from Kumoricon so I have more access to basic needs. However, if I were to stay in a hotel, chances are, I may spend up to 50$ on food, totaling in 100$ altogether.
My advice is try to buy everything on the last day when they have the whole sale going on to try and get rid of everything, that's when you can try and bargain for an item. However, you have to be quick at times because an item can sell out pretty quickly. This wasn't the case for last year since we had a lot of the same item at almost every table... It may be the same this year, or it may not.
As for making money, if you draw, I suggest taking up commissions or trying out for the Artist Alley and getting a table. However, since this is your first con, I wouldn't suggest doing this until you're use to what happens and how things work. ^^;
If you get allowance, try doing your chores and what not. Babysitting jobs are quite popular as well. When I didn't have a job, I pretty relied on art commissions and daily allowances/birthday money/christmas and just saved at least 60-70% of what I got for kumoricon.
Since Kumoricon is in the same hilton in Vancouver, Wa, there's plenty of areas to eat. One is the Saturday market thats literally right next to it (Selling Chinese food, thai food, slushies, and others). There's also an italian ice cream shop near as well, sushi, subway, starbucks, there's quite an amount of food stores around there ^^
There are food in the Dealer's hall but I suggest buying outside for various reasons, one being that it's pretty expensive. LOL.
Honestly, I suggest packing your own lunch if you want to save money. That's what a lot of people do and you'll see some of them having picnics right outside kumoricon as well. If you have friends going, try and set one up so all eat good and for free~
Sorry I wasn't much help for the money making, I'm only experience with how I do it (Which is not as easy as many others). >.<;