#Commodities

Commodity answers to this question become much more profitable, interesting, and educational for readers the further back you go. It's fun to see how gold had a great return in pre-exploration Europe but a huge mistake in the Levant just after 1324 or the US in 1869; of course, the whole reason for the Age of Exploration was willingness to risk the lives of entire flotillas for the profit on spices—mainly pepper, cinnamon, ginger, cloves, cubeb, & galingale—in Europe after the Islamic conquest of Egypt ended Hippalus's direct route to India but before the final crash in the 1660s; cinnamon and cassia were pricy in Ancient Egypt because of their importance in embalming rituals; meanwhile, salt was a lucrative source of trade in West Africa, for Venice, and in China; it was never as crazy as people make it out to be but if you still want to head to 1630s Netherland if you have tulips handy; Napoleon's aluminum dishware stuck with our history buffs enough to have already shown up in 2 answers (one of them even got it right that it was post-1855 Napoleon III and not c. 1810 'Napoleon'); &c. &c. &c.

But 1968? That's already a time with fairly well developed exploration, tech, & markets. You get occasional things like the insane 2006–7 run up in uranium prices (a major Canadian mine flooded) but unit prices in real terms mostly get smaller over time except for short-term bubbles produced by speculators and by attempts to corner certain markets (fake soybeans in 1963; silver in 1979–80; copper in 1995–6; propane in 2004–6; nickel in 2006–7; &c.). Obviously you could make a fortune over a few years from some initial capital by buying up oil ahead of the 1973 OAPEC fiasco. You should certainly avoid cash in favor of securities and commodities during most of the '70s and early '80s. But there's no commodity that's sensibly portable and currently available and cheap that you could sell at a very high markup in '68.

#Electronics

Green's hilarious answer above covers just how complicated this is going to be, at best, and that even the simplest products would be reverse engineered and alter a massive chunk of the future after a 5–10 window. Something as small as a decent spreadsheet program could potentially alter major elections. At worst, you out yourself as a time traveler; you'd spend the rest of your life at a black ops site run by one side of the Cold War. Word getting out of you providing anything useful under torture would mean the other side at best assassinates you; at worst, you survive and they gamble with a nuclear first strike.

#Laptop

Obviously the laptop itself would represent enormous innovations and is thus hugely dangerous. Just keep it hidden, along with your surge protecter and two-prong adapter. What you're aiming for (besides having some decent games, music, and entertainment) is storing databases and algorithms.

You could keep a list of major longshot winners. Without discipline, you'd quickly have the mob or police chasing you after the first few payouts. Here's a list of recent potential time travelers; except for this guy in Staffordshire, they made a lucky hit once and not again or already had a reputation for large low-odd bets. You could hide for a while in major events—Proud Clarion was a 30:1 longshot at the '67 Kentucky Derby—but they don't offer the biggest payouts. More importantly, every win against a casino or bookie is money out of their pockets. What actually works longterm is systematic horse betting, where the house takes a cut off the top of all bets and doesn't care who wins among the punters, as long as their 'luck' isn't so egregious that it stinks of race fixing. By the 1990s, Bill Benter had an algorithm—published in large part by World Scientific—that loses plenty but wins with enough of an edge to beat the system and rake in multimillions. Have a database and a system whose announceable process and copious losses legitimize your winnings, whether legitimate or based on your foreknowledge. (The shifts in track behavior based on your winnings would likely start reforming the races themselves, invalidating the exact records you returned with.)

With enough capital, a similar process could be done with trading algorithms used by hedge funds' automated traders. Run slower or even human-based versions of the same processes and cheats; avoid individual rocket shares but follow investment algorithms that are known to have worked consistently for your expected lifetime. Or, if you treated morality as your characters' dump stat to max out their chutzpah, pull off stock and investment scams before their expected dates. (This might be something a stock-based time traveler would have to default to, as their interference in the market began to shift investment patterns and invalidate the original expected winners.)

The most lucrative patents to take back (assuming you don't want to run your own factories or cripple the internet in its cradle by sitting on most of its processes) are going to be effective pharmaceuticals historically discovered a few years later: taxotere for cancer, lipitor for heart problems, viagra for circulation issues, &c. You can pretend you're a recluse chemist who stumbled across sth by accident. As profitable as they are, however, you're still going to need to take a small lump sum to sign over the patent or sit on it for years as you negotiate with someone who can shepherd it through FDA trials and then mass produce and market it. [You might throw in some patents for AIDS treatment, cheap DNA marker sequencing, and nixing Stanford's treatment of rDNA licensing as a humanitarian gesture, though you might be hard pressed to explain their importance.] The golden age for easy-once-you-know-it patents was the late 19th century; there are still some sitting around though. 1968 is the year a guy at 3M developed the low-tack adhesive that permitted post-its but they didn't figure out how to use it until years later; Lonnie Johnson, Sarah Blakely, and Paul Brown are still decades away from creating supersoakers, Spanx, and valve tops for ketchup and shampoo bottles but any of them could've been made or approximated in '68.

Fads are lightning in a bottle and it's hard to know if you could profit off one by coming in earlier than when they caught the Zeitgeist. Still, you've got waterbeds ('68), pet rocks ('75), mass cocaine running ('75), crack ('84), collectible card games ('93), &c. &c. that you could get an effective and immoral tout to bring out ahead of schedule.