Oh cold I hate those demoralising shopping trips 
I think 12:30-21:30 is a long time between meals, no wonder you are snacking at work - I'd be eating the furniture!!
What about having your main meal at lunchtime and then a lighter meal before work and a light snack afterwards?
Easy ideas for meals that we love in this house:
Chilli and rice - fry mince and onion, add any veg you fancy (we do carrots, peppers and mushrooms but you needn't add any if you don't like the idea), chuck in some tinned chopped tomatoes and some tinned kidney beans in chilli sauce (sainsburys are yum!) and hey presto! I make a huge batch and then that's dinner sorted for three nights.
Pesto salmon - bung pieces of salmon under the grill, turn them halfway through cooking and add a tea spoon of pesto from a jar to the top. Once cooked, serve with new potatoes and veg (Mediterranean like grilled peppers, courgette and aubergine go well - you can get them pre-cooked and frozen from sainsburys and you just bung them in the over from frozen). Again, you can batch cook these.
Mustard chicken - fry some chicken pieces, add a couple of large spoons of whole grain mustard, some low fat creme fraiche and stir gently until warmed through. Serve with rice and veg eg sweetcorn and spinach (I use the frozen stuff again). Can also be batch cooked and served for a couple of nights.
Voila a week's worth of main meals! 