He should take advantage of that deal while he is in tech school. Not "buy everything from Snap On" but "buy some of the tools that they excel at."
What is he planning on working on first of all? Most people here are auto techs (mostly gas/passenger vehicle, with some heavy duty diesel techs too), so a lot of answers will be focused on someone who is going to work at a dealership for Ford, Honda, etc.
Flare/Line Wrenches (whatever you want to call them) are a definite from snap on. Metric 6 piece set is $140 after the 50% discount.
The Extra Long double box end wrenches are also a favorite of mine. Since I got these, I've used a regular wrench just a few times over the past few months (less than 5 times). Cornwell also makes a set, but similar pricing to snap on (and I doubt he has a 50% off offer from cornwell). $150-$200 for a metric set depending on what sizes he needs.
Those would be the two things I would buy from Snap On if I was starting out (maybe I'm forgetting a tool or two).
A lot of people will tell him to buy the Snap On dual 80 ratchets, but I say don't. Yes, they're arguably the best ratchets out there (and I love mine), but there are so many other fantastic ratchets out there too that are way cheaper for a starting auto tech. The Armstrong 88T ratchets, Gearwrench ratchets, the ubiquitous taiwan 72T ratchet (sold under Harbor Freight, Tekton, Kobalt, and almost every other tool brand with imported ratchets) are all fantastic choices. $100 there would get him an excellent set of professional ratchets from somewhere other than Snap On. The gearwrench or Armstrong ratchets he might even be able to warrant with a Matco driver if he has one (same parent company). Plus, if he wants to upgrade at a later time, it's helpful as a tech to have multiple ratchets of the same size/style, so it's not like he would be wasting money on buying a non Snap On ratchet right now.
For combination wrenches Wright, Proto, SK, and Armstrong are all great choices. Wright and Proto have a flank drive plus technology on the open end like Snap On, and SK will be adding that to their regular wrenches before the end of the year. Good quality tools for even less than half off of Snap On.
For chrome sockets, SK, Wright, and Proto again are good choices. Professional quality with out the tool truck markup. Way cheaper too. Pittsburgh Pro also would be a good choice if you really want to spend very little, and I wouldn't feel bad about upgrading them later when he's established himself as a tech. For the $50 you spend on them, the Pittsburgh Pro (not just the regular pittsburgh line) is made in Taiwan, and are probably identical to gearwrench and many other brands that charge way more than them.
Impact sockets again SK, Wright and Proto are good choices for not too much money. Even cheaper is Sunex, who make top class impact sockets that many pro techs love here.
Air tools- For impacts, I'd start off with Harbor Freight's earthquake line up, or I would go for a mini impact (M7 mini impacts, Astro Nano, etc). The earthquakes have been used by tons of professionals here and have held up to tough use. Again, it's not a bad $100 investment vs $250-$300 for an IR or even more for Snap On.
Outside of those tools, he needs to know what he is working on before he starts buying other stuff.