Hey, welcome to EBC! You are in good company, I just got married a few months ago and, like you, sold some of my collection to help pay for the wedding... now I'm selling more stuff to pay off the debt from the wedding! But here's my problem/blessing, my new wife, Melanie, is also way into the Mother series, so we keep keeping things instead of selling them. >_<
Anyway, check out the site http://www.gameswag.com
It has rough estimates of what different collectibles are worth.
I do a decent amount of merch buying and selling. I usually deal more with Mother items than EB, but I'll take a crack at what you got.
Your stuff is roughly worth:
*Game, definitely used but working! - $100ish by itself
*Full-size game box, used but in good shape! It also has the original store price tag. -$80ish, $280+ if you include your game and guide.
*Guide, defintely used, but in good shape! -$60ish
*Nintendo Power advertisements x 2 -Not sure which ones you are talking about, but maybe $15-20ish a piece if you're lucky
*Scratch n' Sniff cards, w/o the sixth contest card - $15ish, good luck, i've been listing mine on eBay for like 2 months
*Scratch n' Sniff card advertisement - $15ish if it's the one I'm thinking.
*Unopened Mach Pizza Air Freshener - A LOT, I'm not too sure but depending on the condition, you could fetch $200+
*Contest winner sheet - Sell this with the air freshener and you'll get mucho dinero
*Game Genie Volume 3, No. 2 with Earthbound codes (highlighted, lol) - Not sure, maybe like $10? Never seen one.
*Super Nintendo, original run poster (the Super Play Action Football, SimCity, Zelda III one) - Sorry, I'm blanking on which poster this is...
*Random Fangamer buttons and stickers from purchasing the Mother 3 guide and the EB'9X shirt - You'd probably get like $20 for the bundle.
I'm being optimistic on most of those. Again, these are just rushed numbers off the top of my head and probably aren't terribly accurate, but it's something to go off of.
Also, I HIGHLY recommend piecing it out and not selling it as a bundle... That being said, I wouldn't be a collector if I didn't make you an offer. I'd give you $400 for all of it.
...don't judge me...