If you're buying Wax Packs, you have three different options right now; a single, random 7", a "hobby pack", which is a package of five 7"s, and a "hobby case", a box containing ten packs. Of course, much like your general pack of hockey cards, the outside packaging on the packs and sleeves is identical, so you don't know what you've got until you open up each record individually.
I'd suggest starting off with the hobby pack if this is something you want to get into. At around $30 shipped, the price is on point with ordering five separate 7"s from a label or distributor or whatever. The pack also comes with a baseball card-sized download card featuring one of the artists/bands in the series (mine was Austin Lucas), so you also get all of the songs from all 10 7"s, and a few bonus tracks. Much like a regular set of cards, there are also the random limited-number inserts, which in this case are colored vinyl. Most colored pressings are under 150 pressings, with some as small as 5, hand numbered. My pack came with the Marathon/Fire When Ready 7" on olive green (10/50), and an extra variant, the Half Hearted Hero purple/splatter variant (3/5), If you buy an entire case, you're also guaranteed to get a test pressing. A few cases also apparently contain download cards with pieces of busted drumheads and cymbals.
An unopened pack, listing all 10 7"s
A standard, baseball card-sized download card
If you're into collecting variants, Secret Audio Club set up a trading forum where you can swap your extras with other people. I'm very happy with the pack I bought. The card itself was pretty cool (I'm a big Austin Lucas fan), the Half Hearted Hero vinyl is one of the coolest pieces I've ever seen, and the other 3 records were ones that I was hoping to get without buying multiple packs (Austin Lucas, PJ Bond/Arliss Nancy, and Such Gold).
Half Hearted Hero purple/splatter pressing, hand numbered out of 5
I'm all for this idea. The bands involved are a pretty decent mix of both cow-punk and melodic hardcore/pop-punk (Such Gold, Banquets, Aspiga), the idea of getting random, very limited colored vinyl is awesome, and merging card collecting with record collecting is pretty much the raddest, dorkiest thing ever. Like I said, I got really lucky to get almost every 7" I'd wanted in the series in the one pack I bought, but I may get another, just to try and get the Banquets 7".
(edit: I've been told that Pentimento actually had to drop out at the last second, so while packaging refers to them in the series, they were replaced by Such Gold)
*fun story. I went to a Red Sox game with my roommate this past summer, and we both bought a pack of cards from our birthyears ('85 and '87) from a vendor outside. Even though he told us to avoid it like the plague, we popped in the pieces of gum. Most horrifying experience ever. They disintigrated into a horrendous tasting powder. Don't try it, kids. Don't. Please don't. I feel like throwing up just talking about it.