noun
suitcase, trunk
A1
Koffer: means 'suitcase' or 'trunk'. Masculine noun (der Koffer) with unchanged plural 'Koffer'. Regular declension (der Koffer, die Koffer; Dativ Plural: den Koffern). Common travel word for a piece of luggage; for individual packing use 'einen Koffer packen'. Also used for larger trunks or storage chests in some contexts.
Examples
Ich packe meinen Koffer.
I'm packing my suitcase.
Der Reisende packte den Koffer, bevor er zum Bahnhof ging.
The traveler packed the suitcase before he went to the station.
Der alte Koffer steht im Keller.
The old trunk is in the basement.
Details
Mnemonics
Imagine a travel suitcase with a big letter K on it at the airport conveyor belt.
Sounds like 'coffer' (a chest) — think of a chest for clothes.
der — imagine a man (der) carrying the suitcase through customs.
Notes
Koffer is a regular masculine noun. Plural is Koffer (no change in spelling).