"From" this to this is an idiom meaning from the start of a meal (or something else) to the end
The same dictionary suggests the metaphor is specifically derived from the .... 
take a back seat - have little or only observational involvement in something - not
... [DOC] [TLE] Proverbs and Sayings - The Idiom Connection [PAR] The politician promised to do many things but he never did anything.