Don't leave it too late , up here most of the shops start changing their clothing ranges from mid June so by July they have pretty much had the end of season sales going a while. It you really see something you like and want to take on holiday just buy it there and then. If after a couple of weeks you see something you prefer more take your first item back to the store fore a refund then buy the other one instead.
Mens t-shirts in Primark (for character ones) are £8-£10 each at the moment and their mens shorts start at about £14.99 up over in lots of colours designs and fabric choices. The womens and kids departments had cute tops and things too starting at about£2.50 and above. They had a few sun dresses from about £15 up over that I walked past last week that looked lovely and plenty of sandals in all colours sizes fits and different heights .