My sister and her family (DDs aged 4 and 18 months) are the absolute models of travelling with children. If she were on here she would say don't worry about the flight, everyone will cope. And, unless you are going somewhere extremely remote or to a developing country, you will be able to hire or buy everything you need.
She makes me feel great about it (which is good cos we love our holidays too!). We're planning Italy for a friends wedding in May next year when our bub#1 will be 8 months.