Can you get in anywhere with a ladder under your arm?
A ladder sounds heavy. I suggest (dependent on the venue) a hi-viz vest, tool box full of grog and a hard hat. This really only works at festivals.
Upvote for http://www.ntoonz.com/Schlock/SchlockLogo-LeftChunk.gif
If you need to avoid a long line, just enter the door you need while wearing a sweater and holding a printer ink cartridge. Pondering expression on the face is required sometimes.
Carry a laptop. Wear a nice-ish suit. Hold a couple of files with random printed paper stuff. Browse them frantically while walking around the office building, while appearing anxious, yet very determined and serious. The very basic stuff we all need to learn at some point to survive the dead-end corporate bullshit.
Be prepared to give an elevator pitch, if necessary. Make an improvised excuse for a random pause in the hall to avoid security. Maybe spill your coffee, maybe flirt with that sexy secretary. Ask the seceretary to look what the racket is in the hall (which you created). Pour her coffee on her keyboard.
Pop into CEO’s office, switch the laptops, if same. If not, just steal his and leave a one with the slimy stuff. Connect a usb bomb-stick with dubious $#1+. Exit ASAP. When far enough from the building and the prying lenses of security cameras, remove your Groucho Marx guise. Exhale and stub out that cigar.