For this occasion
An engagement is the one milestone with no settled rulebook, which is why people search for one. What follows is what’s customary in the UK, in the order it tends to come up, and none of it obliges you to buy a thing. The first page in the list says outright that in plenty of families nobody buys an engagement gift.
The pages here follow the questions in the order people ask them: whether a gift is expected, who gives it, what to write in the card, and what to give if you do want to give something. If you want it to be personal, the engagement gift page covers a portrait made by AI from a photo of the couple, and a photograph printed as it is. You see a free watermarked preview of a portrait before you pay, and nothing prints until you approve it. A Christmas engagement has its own section on the gift page.
And after that
The stage that follows this one is the wedding: The etiquette, the spend, and the words: what a guest is expected to do.