Changing habits is very hard, especially giving up food that has been engineered with the sole purpose to make us crave it.
Cold turkey usually works. Give up chocolate and crisps (even the 99 cal packet) for a whole week.
If you really need a piece, have a thumbnail size piece of 85% chocolate. Otherwise, it is more the sugar you are craving.
You don't need to snack, it is something very British I noticed living here and there. French women do not snack and we have dinner far later than you. Of course it may happen that one day for some reason we eat something, but not usually. And it is more likely to be real food, such as something from a patisserie, than something that comes in a wrapper or a junk food outlet.
Try to abandon the industrial and fried food. Fill up on massive salad and do your own sauce as said cream or other sauces are full of sugars and additives. Add some lentils to your salads or can of tuna in water (not oil) and you are good for the afternoon.
Break the habits. Do you usually have a biscuit or whatever at a certain point of the day or while doing a certain thing (tv, MN,....), make it a thing to only eat sitting at a table and eating with a fork and knife. You wouldn't eat crisps with a fork.
Especially if you have kids, make it a family habit. to eat real food, sitting down.
You are not only dieting. You are changing your lifestyle forever, otherwise the second you go back to eating the way you did, the weight comes back up with usually a big bonus.
Right now you have a goal, your holiday, so you are more drastic, but I would recommend, change lifestyle, adopt the Mediterranean diet, eat more plants and not what comes out of a factory plant.
Read the ingredients. Anything over one line, leave it on the shelf. Anything you wouldn't be able to do in you kitchen without huge machines breaking down the components, leave on the shelf.