Keep steel dry, and apply wax or oil to prevent rust. Any steel can rust under the right conditions, including stainless. High carbon is more prone to rusting.
Do not store the blades in leather sheaths for extended times. Leather needs a slightly acidic pH to remain high quality, and the pH combined with moisture from the air leads to corrosion.
Do NOT use harsh chemicals like alcohol, bleach, hand sanitizer, acetone, etc. These can ruin even the highest quality leather very quickly, either by damaging the finish or the leather itself. If dirty clean with a dry or wet towel.
Its not a good idea to store in direct sunlight for extended periods. Leather is after all skin, and just like our own skin the sun isn't good for it in excess. It can darken, harden, dry it out, and bleach colors.
Periodically apply a leather conditioner. How often to apply depends on the product and the environment you use it in. I've conditioned my wallet once in the last year. Conditioners help keep the leather grains lubricated which prevents drying and cracking. Leather conditioner can be purchased from us, in various department store, or online.
If the jewelry is made of natural products like wood, leather, bone, etc then its best to keep it dry. Moisture can break it down prematurely. You can apply a wax coating (available through us, or online) to help protect it from water.
If its made from leather follow the guide above in the "leather" section.
If its made from iron/carbon steel, brass, bronze, silver, copper, or any other material that naturally patinas or corrodes, you can use a coating like clear lacquer, or wax to slow down the patina. Or you can allow a patina to develop, which gives it more character in my opinion.