Hide and/or steal the tissues.
The missing tissues are a two-fold gift. It makes things harder for those who will be seeking tissues (i.e. less productivity!), and spreads biological contagions may have otherwise been thwarted by the tissues. Biological contagions are the prank monkey’s best friend, as they are a set it and forget it tool. Productivity is affected by lost time seeking tissues, time spent complaining there are no tissues, and in employee sick time.
If you are afraid of contracting the contagions yourself, replace nice tissues with the cheapest one ply brand you can find. This should stave away the contagious matter, and simultaneously worsen the day of those who need to blow. Enjoy the raw red noses as they appear.
For a festive touch, do this prank in December and feel like Rudolph is all around you.