You can use mineral oil or any cooking oil you have laying around the kitchen. Mineral oil is the best option because it does not spoil. Cooking oil works just fine for the knives but does spoil over time and will become very gummy and sticky on the knife. If you use cooking oil make sure to clean the knives and replace the oil every month or so if they aren't going to get used for a longer period of time.
You can check out our knife oil HERE if you'd like to grab an easy oil solution.