My first rail journey for 2012 was on the 5th Jan on Eurostar 9180 06:50 London St Pancras - Bruxelles Midi/Zuid on a trip to Luxembourg, I went "round the back" via Liège and Gouvy outwards, then direct on the mainline via Arlon and Namur on the return.
London St Pancras - Bruxelles M/Z (Eurostar class 373 TGV-TMST)
Bruxelles M/Z - Liège-Guillemins (DB class 406 ICE 3M EMU)
Liège-Guillemins- Trois-Ponts (CFL 3000 electric loco + SNCB I10 carriages)
Trois-Ponts - Gouvy (replacement bus)
Gouvy - Troisvierges (CFL 2000 EMU)
Troisvierges - Luxembourg (CFL 4000 TRAXX electric loco + DOSTO double deck carriages)
Luxembourg - Bruxelles M/Z (SNCB AM96 EMU)
Bruxelles M/Z - London St Pancras (Eurostar class 373 TGV-TMST)
I also had an hour before needing to check in for my return Eurostar service to the UK, so got some trips on both the old AM62 EMUs and the new HLE 18 Sprinter electric locos on the Jonction Nord-Midi a couple of times.
However, my first genuine journey in the UK was with First Capital Connect on a class 313 between Highbury & Islington and Moorgate on the Northern City Line a couple of days afterwards.