Hi Sami,
I am sure that someone will be able to give you better advice, but the shakes could be your body reacting to being at a lower blood sugar than it is used to being at. This is how it works with T1s (not saying that you are T1, just a similar theory) ie people who tend to have high blood sugar most of the time can feel hypo at higher levels, whereas those who run at low blood sugars, can sometimes lose sensation of hypos a bit, becasue their body is used to running at that level.
I guess the only thing you can do, is have a word with the supermarket, and see how they can accomodate your diabetes...they should make allowances, to allow you to eat regular meals etc. There is something in teh disability discrimination legislaton about this I believe, but hopefully, a word with your supervisor, expalining teh situation might sort it out? Cold can effect your blood sugar too