Unfortunately for this project, but fortunately for my family, we closed on a new house on Dec 23rd. This meant that we started moving on the day after Christmas -- a process which will likely be ongoing for at least a couple more weeks -- and I didn't get to build this project in time to participate in the Trinket Everyday Carry contest.
However, I still intend to work on it as time allows. Since the contest is over, I might use an ATTiny85-based DigiSpark board instead of the Trinket Pro. It should be more than capable for the simple needs I have. And if my µC chops were more up-to-snuff, I could probably do it with an ATTiny45 or 25.