I take
Bagels + minibell cheese. Can't crush a bagel + cheese stays wrapped.
Microwave Porridge oats x 2 packets per breakfast.
Pasta in a mug, just add boiling water, better than the soups + add cheese.
Instant potato, quick cook pasta, noodles or rice meals.
Packets of tuna, different flavours available.
For quick cook pasta. Heat pan to boiling, cover with towel, hat or pot cosy. Re heat after 5 minutes, takes twice as long but does cook, same applies to rice meals.
Instant custard plus dried fruit or fruit cake.
Sachets of hot chocolate drink of many different types.
Condensed milk in a tube. With porridge, hot drinks and with the custard and fruit.

During the day
Fruit cake, mixed nuts, dried fruit, shortbread, oat cakes, biscuits.

Basically I check the calorie content, looking for 300Cals / 100g or better.

Of course, pub grub and fruit when available. Sandwiches from shops.

Each to their own of course but it works for me.

Colin