Curry leaves: absolutely fantastic flavour when fresh, don’t even bother with the dried ones. I’ve only found fresh ones in Asian supermarkets, but they come in big bags and freeze really well. They can be used within about 5 minutes of coming out of the freezer.
Toasted ground rice: Make by dry-frying some raw white rice until they go light brown. Can then be kept for ages.
Lime leaves: could not live without them, again don’t bother with dried. Can be bought frozen from Asian supermarkets and then can be kept in the freezer for ages.
Vietnamese coriander (rau ram): Lovely unusual-looking herb used in salads and soups. Growing it on my balcony in London and it seems to be going ok. Also called Vietnamese Mint.