Hia Swift83! Probably nothing. Hanging baskets are tricky because they dry out so quickly, especially in this hot weather we've been having. You really need to water them in the evening when the sun has gone down but best of all take them down and soak them for a while in a suitable container (I use a washing up bowl). They also need regular feeding and dead-heading but if you are house minding I wouldn't say that was your problem.
If your friends aren't back yet, you can probably improve the look of the baskets by removing the dead heads of the flowers and soaking the entire baskets as I suggested, but be warned if they are really dry they might float at first! If you do have some plant fertilizer it won't hurt to use it either!!!
What a good friend you are - I hope they buy you a little gift when they return.