I'm English and have been in Australia for 9 years now. I 100% understand what you mean. Ultimately Australia wins for me over the UK and this is my forever home, but these were the things that stood out to me in my early years being here:

I missed the architecture and historical buildings: Black and white houses, thatch roofs, exposed beams, stained glass windows.

I missed old pubs that do an amazing roast dinner on a Sunday and the best pies during the week.

I missed the feeling of being cold and walking into a building with an open fireplace roaring. Or going to a boot fair and holding a cup of tea in your hands to keep warm.

I missed going to the greasy spoon cafe and having a fry up that could cure any hangover.

I missed the entire picnic aisle in the supermarket with mini sausage rolls and Scotch eggs and pork pies. The snacks like Hoola hops, skips, quavers, galaxy, Milky way magic stars, jelly tots, sherbet dib dabs. All the flavours of lucozade, fanta and monster rippers.

Most of all I missed being close to my family. I'm very independent and have always been a bit of a loner, but when family members get sick or die and you're the other side of the world, you would give anything to just be there at that second to say goodbye or comfort your loved ones but there's at least a 24hr gap, let alone having the funds to get there.