Put your master's degree to good use by chasing undergraduates through the library for their blatant disregard of your food policy.
As coffee shops are becoming the norm in today's libraries, many institutions are rethinking those food policies. Be sure to keep some restrictions on food and drinks so that you'll still have something to be annoying about.
"No lid on your coffee cup, young man?!"
"Is that a spillproof container?!"
"Is that thermos ALA-approved!?"