Box of balloons, with the featherlight touch
Pack of party poppers, that pop in the night
This verse shows the young boy clearly embarrassed at buying such an adult product for the first time. He describes them to the cashier of the chemists by as many different ways as he can, without actually saying what he wants.
Condoms make for surprisingly strong balloons. Featherlite are a brand of condom made by Durex.