。
She plunked the shopping bags down on the table with a thud.
Literal
Shopping-bags [object-を] thud [adverbial-と] table [possessive-の] top [on-に] placed.
どすん is a mimetic for a heavy thud — the sound of something weighty being dropped or set down forcefully. と marks it as an adverbial describing the manner of placing. 買い物袋 ('shopping bags') and テーブルの上に ('on the table') set the domestic scene. The mimetic does all the expressive work — without it, the sentence is neutral; with it, you hear the weight and frustration.