[GeeTwo]

(Emphasis mine)

Originally Posted by David Brinza

In 2015, teams were required to bring their withholding allowance items into the pits during robot load-in. Going to the trailer or build site after load-in was not permitted. Robot inspectors would ask teams with a significant amount of fabricated items declared as "withhold allowance" to weigh them at the inspection station.

Where was that, exactly? I've re-read the 2015 rules with specific emphasis on R12-R17 (Fabrication Schedule and Material Utilization),and T12 (during the event). Neither the word trailer nor the phrase build site appear anywhere in the game manual. I can't find any rules prohibiting access to a trailer or build site for the purposes of (for example) getting COTS parts, tools, non-robot items (such as costumes, buttons, and office supplies) , or excepted assemblies at the end of R17. The key rules regarding fabricated items at the tournament were:

Originally Posted by 2015 Game Manual, R17

At an Event, Teams may have access to a static set of FABRICATED ITEMS, not bagged per R14, known as the WITHHOLDING ALLOWANCE, that shall not exceed 30 lbs. to be used to repair and/or upgrade their ROBOT. The WITHHOLDING ALLOWANCE may only be brought into the Venue when the Team initially loads in at the Event. Items made at an Event do not count towards this weight limit.
For Teams attending 2-Day Events, these FABRICATED ITEMS may be used during the Robot Access Period and/or brought to the Event, but the total weight may not exceed 30 lbs. FABRICATED ITEMS constructed during the Robot Access Period and bagged with the ROBOT are exempt from this limit.
Items exempt from this limit are:

• A. the OPERATOR CONSOLE,
• B. any ROBOT battery assemblies (as described in R4).

Originally Posted by 2015 Game Manual, T12

During the event, from load-in on the first day to load-out on the final day, Teams may only produce FABRICATED ITEMS in the pit areas or provided machine shops, as defined in the Administrative Manual, Section 4.8: The Pit, and per R17 in Section 4.6: Material Utilization.

Bottom line: During an event, you may not fabricate items for use on the robot except at the designated locations and times within the venue, nor bring fabricated items for use on the robot into the venue except at check-in, either in the robot bag or the withholding allowance.

An interesting subtlety I noticed on this search is that while "FABRICATED items consisting of one COTS electrical device (e.g. a motor or motor controller), connectors, and any materials used to secure and insulate those connectors" created before build season were permitted on the robot (or in the withholding) under R12, they were not exempt from being part of the withholding allowance under R17.