i would use a very little piece of wet papper towel.
this guy has the right idea.
sometimes ill have bud in my jar that gets a little too dry. to fix this ill add a drop or two of water onto the top. a wet paper towel will work too. especially if its a large amount of buds like you have. If you feel like they are not getting enough moisture by themselves in the jar then add a couple drops. if thats not working put that moist paper towel inside an open ziplock bag(so the buds dont touch the paper towel) in the jar. ive also heard lettuce will work and not leave a flavor. some people even use fresh mj leaves.
when you do this though you MUST watch your buds. you cant just do this and leave for work or something because they can EASILY get too wet. check on it every couple of hours and give it fresh air.
orange and lemon slices do work very well. but i only suggest these if you do not care about the smell/taste of your bud.