Manage costs of a farewell party

After 15 years at the same company, your friend and coworker is leaving for another position elsewhere. It's disappointing to all of you who worked with her over the years, but you want to send her off in style. You quietly being to plan a farewell party and find that you need some financial help from your coworkers. They're willing, but keep forgetting to bring in cash or their checkbooks and you're trying to keep from talking openly about it in front of your departing coworker. You need a quiet way to collect money from the people who can make it to the party.