Why the blue blistering blazes would you want to listen to MP3s at a music festival?
The walkie talkie might be good if the batteries lasted 5 days, otherwise its clutter.
To find yer tent molish a unique flag and stick it on a long pole. Paint the tent with coloured waterproofer. One red tent in a field of beige ones is easy to find.
If you leave yer bits at home, they won't get nicked.
Wellies, some sleeping gear, condoms, and perhaps coffee (though people mostly buy that now) . There are 362 days a year to play with yer ipud.