Pickles would be the easiest, or add sweet onion slices thin slices carrots. At first I thought what the heck is the spring for? Never saw that before. I guess to hold down the beg? If you fill the jar, unnecessary. You can also add peppers. Hint a splash of pineapple juice will add a nice flavor and sweetness. Any pickle recipe I ever saw called for too much salt and vinegar. Less is always better and just keep in the fridge.
The spring is just to make it foolproof.
Canned foods generally go in hot and create a vacuum when they cool. Fermented foods generally go in at room temperature and do the opposite due to gases releasing during the fermentation process. They create pressure instead so the spring allows gases to escape but don't allow any air to get sucked in(like at night when the room cools off). It's like a check valve.
You can tighten a regular lid about the same as when canning and it will work fine because it will allow pressure release but vacuum will pull the lid down and the gasket will seal it but not so tight pressure can't release again.
There are people who make homemade wine in the plastic bottles that 100% fruit drink comes in and they just lightly snug the cap. Wine is fermentation and acts the same as any other type. Bubbles/gases must escape but you don't want air with possible airborne fungi to get sucked in.
My wife brought home some “cucumber salad” from one of her friends a couple weeks ago:
It was actually thin cucumber and sweet onion slices in the “broth” — lightly tangy, slightly peppery — really good, and I think you are right, part of the reason it was so good is because the salt and vinegar was not overdone. Granted, I’m not big at all on strong vinegary tastes.
When the solids were eaten, I dumped in some slices of Roma tomatoes. Normally, Romas are too bland for me except as a sauce base, etc., but, after an overnight soak, this “broth” livened them up very nicely.
I’ve been bugging wifey for two weeks to “get that recipe”, but, no dice yet. She (wifey) is on vacation next week, so, I’m gonna pester her some more. ;-)