I would highly recommend that you NOT carry any gas in your trunk.
If you fill in Fallon, you will make it to Ely no problem - fill in Ely and you will make it to Richfield no problem. I've made that exact run going west and that's what I did - and I drive a full size pickup. I know for a fact that what gas there is between Fallon and Ely costs about 50 cents a gallon more. I don't remember any gas between the NV/UT state line and Delta.
On I-70 there's no gas or cell service between Salina and Green River. I think there's one pullout with portapotties, other than that there is absolutely no civilization along that stretch.
You will make good time on US-50. Speed limit in NV is mostly 70 and mostly 65 in UT. Ely would make an excellent lunch stop.