I stopped drinking soda many years ago (apart from the odd coke at a party or something). Realised it was addictive. It just feels normal to always be drinking water now. I don't miss it.
Coffee, I turn my machine on in the morning and it's 50/50 if I remember to drink one during the day. I drink a fair amount of tea (PG Tips with milk, I'm English) though.
If you are a big coffee drinker then start during a weekend where you can get through coming off coffee. Headaches and a mind like molassis are a hard way to go through th work day.
Otherwise it's coffee in the morning, I'm a developer after all, code isn't going to magic itself out of thin air, it needs coffee! :-)
No you wouldn't collapse, the body stores fat exactly for this reason. When you fast, eventually your body switches to fat burning mode.