Do you stay at the cottage the whole time or do you go out and about?
Why not stop on the way there and pick up food for the week. Make it really easy and limit the amount of washing up. Unless your children are very very young then they can help tidy after themselves.
I would do the following.
Breakfasts - choc chip brioche, crumpets, pancakes, fruit, croissants, small cartons of juice, none of this needs a plate pop it on a square of kitchen roll and bin when done. This means that all breakfast options are literally pick up and eat. Unless the kids are under 2.5 they should be able to manage to get breakfast with little input from you.
Lunch - have quiche, pork pies, cheese, mini sausages, sliced meats, bread, crackers, fruit, salad veg like cucumber tomatoes, humous, chutney crisps etc. Again no real crockery needed either buy paper plates or put everything outbox a couple of plates in centre of the table a d everyone takes what they want.
Dinner - cooked chicken, bag of salad and a nice crusty loaf, pizza and salad, variation on the lunchtime with added olives etc, quiche with salad, jacket potatoes, buy decent sub type rolls and fill with cooked meats salad etc and have with potato salad and coleslawhave dinner out a couple of times even if it is just a chippy sat in a bench. Buy a disposable bbq and do sausages and burgers one night, eat off napkins no washing up.
The most important thing is to set your boundaries with your husband and be clear exactly how much you are willing to do. He needs to help with the planning, make it very clear that sandwiches 3 times a day for 7 days is not going to happen. No reason why can't do sandwiches a couple of times though. A decent sandwich with some fruit and a pack of crisps or biscuit is an ideal lunch.
People aren't trying to be nasty when saying you are being a martyr. They are just trying to show you that you don't have to do 3 proper meals involving lots of planning and washing up every day. You just need to have a proper conversation with your husband.