I make my own products and sell them.
Imo your approach is completely wrong, if you are on a forum asking for ideas then making your own products to sell isn't for you.
If you make your own products they should be related to something you are interested in or to solve a problem you've come across.
Look at John as a prime example, people buy his knives and pens because they are something he is interested in and shows that, if x-corp or x-small-business started making a product like that but had zero interest in it other than they want to make a product that'll turn a profit then they would sell some for sure if it was a good product, but they wouldn't gain the sort of following and level of sales he has.
Also while he certainly seems to shift a decent number of knives and pens I doubt he's especially well off because of it, look at how many new and generally very high end machines he buys and how many people work for him, yes his business has grown but so have the overheads and signficantly so, don't assume you'll get rich doing something like he has, I like John too but I genuinly worry he's one recession away from having to lay off a load of staff and cut back drastically or risk actually running out of money, if I were him I'd curb the machine splurge and focus on building up retained profit using what he has for a while.