Your goal with any opening promotion is to 1) get noticed by potential customers and 2) develop a repeat pattern of behavior in your customer base. Drive them to your location, get them to start using your beverage terminology, and emphasize those products that are most advantageous to your business model.
It's difficult to define the recommended promotion without first learning more about your marketing strategy. What differentiates you from your on-site, off-site and home competition? Develop a promotional event that emphasizes those differences and starts your customers buying your products in the manner that you prefer; for example, have you ever considered why we as American consumers feel the urge to purchase a soft drink and French fries with a hamburger?
Our behavior has been patterned by McDonald's and others to believe that these three items are necessary at every meal, largely because it maximizes their profits on every transaction. Every photo in-store shows the three items together, we are bombarded by advertisements showing happy consumers enjoying the combination and products are grouped on the menu for consumers to select. An effective promotion in this scenario may involve the launch of a "combo meal" or other limited time offer that supports the buying habits that the company wishes to develop.
This is, of course, a much larger scale example that one single coffee business on a college campus, but the same rules apply. In the case that your competitive strategy emphasizes quality over the standard quality of products available at Starbucks and the other fast food chains, you should develop an event that showcases that quality and allows customers to sample them in a low-pressure environment. Perhaps a taste test with some financial incentive (try our coffee, complete a survey and receive a $5.00 discount card for future purchases), from which you can collect data for use in future advertising and promotions "95% of Starbucks drinkers prefer Happy Chick Coffee at xyz college campus."
In this case, you 1) get attention 2) have customers trying product 3) receive valuable feedback from those customer and 4) offer a future discount that will increase the likelihood of returning for future transactions (also reinforcing the pattern of use). Not bad for an opening day's event. It's not the "balloons, confetti, clowns and local garage band" idea where most bad businesses waste their marketing money.
Or, depending on your strategy, the most effective promotions may be very different.
Tell us more about your business and we can make other suggestions that may help.
Best of success,
Andrew
