Invest Responsibly
Although the world of stock perks can be fun, it can also be dangerous to just buy stocks based on the perks. Most of what is here is probably common sense, but just in case I'll write a few things that you should always keep in mind.
Research and buy good companies!
The most important strategy is to buy a stock because you think it's a good investment, the perk is just a nice bonus. Do your research, look at the IR and research reports. Buy a company that you think has a good future, or at the very least won't have a downturn. Plenty of unhealthy companies offer benefits and just buying them for the perk is a great way to lose your principal investment. Of course, if you really, really want a perk or think that the risk of the company turning around is acceptable, then go for it, just know what you're getting into!
Don't spend money just for perks!
Some people only look at the overall yield of what the perks give you compared to the investment. Although in some cases it can be surprisingly high, in the end the perk will be a horrible 'purchase'. I've seen people complain about having to spend 100,000yen to get 2,000yen worth of product, and that's not how you want to look at things! The perks are a nice bonus for putting your faith in the company, something that you can hopefully receive on a regular basis. Look into it as normal investing first, with the hope that you'll make money by the stock price rising along with getting some presents.
Perks can be removed or changed anytime!
Similar to a dividend, companies can choose to discontinue or make a change for the worse to their benefit system. It happens all the time and is something you have to keep in mind when looking at them. I've seen announcements of negative changes days before the rights date, although it is incredibly rare for it to be changed after then. For some stocks, there are a lot of investors who only really care about the perks so a removal or negative change can tank the stock price!
Here are some examples:
Take a guess on what day they announced bad news regarding the perks. There's always the risk of this happening, so either focus on investing in strong companies that happen to have perks, or be prepared to take on the risk if it's a perk that you really want!