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I don't know about useful, but I have all the EV charging things, TeslaMods.com, TeslaTap.com, the Valet page from TeslaAccessories.com, Tesla itself (which my DES added initially when I got the car), and probably a couple of others I'm forgetting. But I have an iPad (frequently with me) and iPhone (always with me) with these things bookmarked, plus the various apps for some of these sites--the ones that have apps--on both devices...so I dunno how useful these are. I presume some may be useful on trips, but I'll take my iPad and iPhone on trips. I guess my point is, I figure these are useful to be able to get to, but whether from car or other mobile device, it doesn't matter. Except the valet instructions (which a couple of other sites may have, too, methinks--I'm not sure which set of valet instructions I like best...never had to use them).
I'm probably missing something--I copied these from my home bookmarks (at home I have 3 threads here bookmarked as well, to do with charging and road trips) so the list above might be slightly "off" compared to what's in the car.