Iphone stuff:
Road trip to record mileage (can't remember price but it was about £2 when I bought it) - can backup to Dropbox and can record more than one car on it.
I use mine at every fill up.
M8 - free satnav that works quite well
My Gas - free price checker on petrol stations near you
I find most of the traffic apps quite poor so won't mention those
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