According to the Virgin Trains timetable, website, and the NRE website, there is no evening meal service. You are likely to be restricted to a choice of a chicken sandwich or 'deli snacks'.
I have never travelled on the 18:46 because it is tediously slow, but whenever I have seen it at Stafford or Crewe it has been surprisingly empty in both first and standard class (when I first saw it I thought it was a broken down train as I couldn't spot any passengers!). It appears to function primarily as a commuter service for Milton Keynes and Rugby passengers (although first class passengers travelling to Rugby would be better off on the 18:33 evening meal service). It bewilders me that Virgin offer some (rather expensive!) first class Advance tickets for travel through to Stafford, Crewe, etc.
When you travel, it would be good if you could let us know how many passengers (as a proportion) remain on the train past Rugby.
For future reference, if travelling to Crewe you are better off travelling on the 18:10 ex Euston (£48 for a 1ST AP vs. £91 for the 18:46 ex. Euston) - which is one of two trains a day to have the high quality 'Bryn Williams' evening meal - and this connects at Crewe with the 20:09 for Warrington, Wigan and Preston, with 1ST AP fares of £42, £43 and £43 respectively (oddly, they are lower than the fare to Crewe only, even though you get the evening meal on the 18:10 ex Euston plus the late evening offering on the 20:09).
