Staring at your stash of shakes won't get you started but having a definite plan to make them part of your life again will....
I usually recommend a structured week of phasing in Cambridge packs and phasing out food!
So 1 pack and two meals on days 1 and 2 (1200 cal in yellow book)
2 packs and 1 meal on days 3 and 4 (1000 cal in yellow book)
3 packs and 1 meal on days 5 and 6 (790 cal in yellow book)
Then Sole source on day 7!
Work your way up with the water over the course of the week as you eat less.... drink more!
It's the least painful way of getting on to sole source I know!
Hope that this helps!