“Developed primarily in the United States, early drum kits were known as traps kits (short for trappings) and usually consisted of a bass drum, a snare drum on a stand, a small cymbal and other small percussion instruments mounted on the bass drum or a small table, all played with drum sticks or brushes except for the bass drum.” — Wikipedia\
“A synonym for “drum kit” this term was used earlier, when drums and percussion were beginning to be assembled into a single “station,” playable by one drummer. The story goes that early kits contained a tray that held percussion “contraptions,” such as cowbells, whistles, and other items. “Contraptions” was shortened to “trap,” eventually becoming “trap kit”.” –Sweetwater Sound
Segarini: Don't Believe a Word I Say 