Does anyone know if I would have any problems if I booked two one-way flights for my US trip as opposed to a return flight? i.e. would I get hassle on arrival with a J-1 visa holding a one-way ticket to California, even if I had another flight booked (e.g. from New York) to return to the UK?
Shouldn't be a problem. Maybe just a "random" search when going through security.
*Just kidding on the random search. You should be fine.
I am hoping to take a holiday after my placement, and so it would be handy to be able to fly home from a different airport... any tips?
If you really want to see a few places, can you do a short trip before placement and another longer holiday one after? Or do like a "long-weekend getaway" kind of deal during the placement?
Also, from your list of places, not sure if you could (have time/money/willingness) hop through Kentucky and/or swing through Florida on your way to New York?
I don't think you would have a problem - you would still be able to show an outward route if asked. Your bigger problem may be getting one way flights that are cheaper than a return. Some airlines have a horrible pricing structure where a one way is about 80% of the price of a return to the same city.
Yeah, that. One-ways tickets are often stupid expensive, and though you could do it, you're technically not supposed to buy a return ticket because it's lower cost knowing that you will not actually fly on the return leg.
--
It could get kind of tricky, but if you know you want to vacation in New York, it could end up being cheapest to buy two round trip tickets: first ticket for UK-NY, second ticket for NY-LA. The first ticket will be for the UK to USA and back portion of the trips, and since the second ticket will be purchased separately, you could get the second ticket so that you go to NY from LA a few days before the first ticket, thus giving you the holiday time you want in NY. You layovr at NY on your way to LA, then after your placement, fly to NY on round trip ticket 2, stay a few days, and return to UK on round trip ticket 1.
Only issue with that is you're constrained to flying through NY on both directions, and you'll be stuck with that route even if you change your mind later.
You can also call up the airline and ask to see how much adding an additional leg on the return trip would be. If they allow it, they'll often tack on a little bit of a fee, but would still be much cheaper than buying individual single trip tickets.
Also, use passport as ID. You may get lucky and a TSA agent will take your British ID, but it's usually passport or bust for non US/Canada IDs.