Frags would be good if you had the profession. Small energy cells are good too but Electronic parts are a hassle to get.
El. parts isn't so annyoning, you'll get ~16 or ~18 el. parts for one go.
50 small energy cells = 500 caps.
Well, I tryed to make small energy cells, metal+alloy=360 caps.
2 El. parts =very low, can't remember, may be 14 caps per 1, so you getting ~100 caps more, if crafting small energy cells and then sell them, instead of selling raw materials.
BUT it'll be faster to not gather el. parts, but gather anything else (minerals/ore no matter) and then make gunpowder/meta/allloy(no matter again) and sell it... better than small energy cells.
About frag grenades, it was an excellent choice before update, now it's x5, 104 caps each, so it's 520 caps.
Requirements:
1 Junk, 1 Metal Part ( 2 iron ores), 5 Minerals.
Are you sure?
2 Junk, 1 Metal part and 5 Gunpowder.
So it's 60x5+120+forgotx2=420+x2 caps.
As I can remember 1 junk is 25 caps, may be not... so it's 470 caps.
520-470=50 caps income, isn't so much...