Small boat cooking can be a challenge. I spent a wonderful summer on a Catalina 22 pop-top sailboat with a girl friend about fifteen years ago. Cooler, no fridge, horrible alcohol cooker and a grill. It is well that I'm an early riser as my GF couldn't function without coffee and it took half an hour to perc a pot on the alcohol burner. Everything else was made ahead or done on the grill. Not so very different from the small cabin cruiser you describe.
Good food storage has become more accessible over time. Really good insulated coolers like those from Yeti are so much better than the Igloos and Colemans we grew up with. Although expensive they are so robust that over time they are cheaper: no costs for replacement handles, hinges, latches, and hold downs. For preparation at home an inexpensive vacuum sealer like those from Foodsaver make a big difference in food life. The days of 'burping' a Rubbermaid or Tupperware container are primitive compared to silicone sealed latching containers like those from Lock-n-Lock. Absolutely life changing aboard in the pantry, fridge, and freezer.
At home and on my own boat I try to avoid waste. On delivery there is more. For example if departure is close enough to home I'll make up casseroles (lasagna, tuna, goulash) ahead in disposable tins or vacuum sealed bags and freeze them hard. Lasagna is just too much work underway but cooking it is easy and it is always well received. A couple of hard frozen 8x8 tins of hard frozen casseroles wrapped in foul weather gear and other clothes will even survive a short plane flight. I've shown up at a boat where the freezer wasn't working and schmoozed some space in a local restaurant freezer until we could get systems sorted.
I usually rotate breakfasts between cooked (not quite full English, but close) and cold yogurt and fruit and maybe cereal. Some places in the world cereal is hideously expensive. In much of the Caribbean I'll buy Grape-Nuts at home and carry it in. *grin* Great with yogurt. I bake bacon in one and two pound batches and refrigerate it in bags to use as needed: breakfast, salads, some entrees....
Nothing wrong with sandwiches. You can freeze lunch meats and extend availability. Frozen cheese isn't great but better than nothing. When the lettuce gives out you can grow your own sprouts for a little green crunch.
Definitely planning. No planning survives contact with the enemy and in our case the "enemy" is the sea.
When crossing international borders you really have to pay attention to limits on food. Certainly anything that might attract fruit flies (not because of the fruit flies - they are just a measure of sensitivity) is an issue. Fruit and veg are limited to avoid insect, bacteria, and virus that might affect local agriculture. Generally whole fruit and veg are an issue but prepared foods are not. Since you have to buy food to account for delays that may not be endured there is a lot of food prep the day before landfall. Coleslaw, mashed potato, maybe fruit salad, soups -- cross your fingers for settled weather otherwise perfectly good food goes over the side. Cans and frozen are usually okay. @BubbleheadChef referred to this in some of his posts.
