If you anticipate being away from your account for an extended period of time, you can activate "Vacation Mode" in your account. By putting your account in Vacation Mode, your items aren't able to be purchased or engaged with by other users. Your items will become available again as soon as you turn Vacation Mode off.
SidelineSwap also automatically puts accounts that have been inactive for 30+ days in Vacation Mode. "Inactive" in this context means that you have not logged into your account for 30 days.
You can toggle vacation mode on and off here: https://sidelineswap.com/settings/vacation