Puy lentils and baked beans are definitely not allowed on Bootcamp!
Some ideas for shopping:
Meat/fish - go for fattier cuts or types of fish. So for example, if you're buying mince, go for the 12-15% fat version, not the lean ones. Buy chicken thighs rather than breasts (and eat the skin!) or roast a whole chicken, slathered in oil/butter, so that the skin goes lovely and crispy, and eat that.
Pork belly is absolutely fabulous, slow roasted till it starts to fall apart.
And lamb chops - but eat all the fat too!
Try and avoid things like ready-made burgers, as well as bacon and sausages, and cooked ham, as they're processed; you can have them occasionally but not at every meal/every day
Cauliflower rice/couscous is lovely home-mdi (the sachet stuff is vile). Just pulse it in your food processor, or grate on a box grater. No need to ring it out in a tea towel.
Celeriac makes a very good potato substitute, either as a mash (even lovely with cooked leeks stirred through), or in a dauphinois/gratin. some lovely recipes on the Bootcamp recipe thread.
Eggs will always be your friend, but don't have them cooked the same way every time as that will soon get really dull. Hard boiled mashed with butter or Boursin is a Bootcamp favourite, and I also love a cheese omelette.