Ooh, have fun! :o
Some kind of identifier for your tent is a good idea (flag/location/position), so it doesn't get lost amongst the millions, especially if yours is a popular make of tent.
Get to the camping area as early as you can to get a pitch - I hate having to spend hours searching for a clear square foot of land to stick my tent on!
Go lightweight as possible, never been to the IOW but if it's like every other festival I've been to you will have to carry everything from the car to the camping area, which may be a long way away!
Having said that, last year we took some cheapo solar markers with us and put them around the tent, helped us find our way and stopped others tripping over the guy ropes!
Take loo roll and money. If you are organised enough to cook, that's great, but bear in mind the tents end up being very close together and space will be at a premium - and everyone WILL trample straight through your pitch, stumbling over guys etc. - pre-DD (who won't eat any festival food beyond sausages so we have to bring a few bits for her to prevent scurvy setting in) we always threw money at the problem and bought our food from the stalls. Less to pack/wash up too :)
Ear plugs a must. People will stagger back drunkenly at night, trip over your guy ropes (see above) and have loud conversations from what sounds like outside your door but is actually several tents away.
Personally I'd bring a hat/headband and wetwipes and forget showering for the weekend, I've never had a festival shower that wasn't icy cold except for Glasto, and they were mixed.... (different set of issues altogether!). The IoW may be better organised, but I nearly died of frostbite at Latitude last year after a 'warm' (hah!) shower, so be warned!
Have a great time :)