I doubt if you are earning your max lifetime earnings at Publix or that you will be with them for your entire career so it's just a start. Don't sweat it - just don't put your funds into Stable Value and get a 0.025% annual return. You have much bigger decisions in life than this..
Do your asset allocation, and then you can pick your funds. A middle of the road allocation might be:
40% s&p500 index
10% midcap index
05% Royce pen
20% American europac
20% pimco
05% stable value
I agree you don't want to put all your money in Publix stock. Altho if your confident of the company, put 4 - 5% in it.
I'm not gonna give you a bunch of useless jargon, but at 19 your focus should be aggressive in growth and small cap stocks. You have until you're in your mid 40s before you try to start getting safer. At your age you need as much growth as you can get because you won't have that time later on in life.
I'm 19 and recently reached the requirements to start my 401k at publix. My choices are Publix Stock, Invesco Stable Value Trust, PIMCO total return, T Rowe price value fund, SSgA S&P 500 Index fund class e, T Rowe price blue chip growth fund, SSgA S&P Midcap Index, Royce Penn Mutual fund, American europac fund, SSgA Conservative Strateq, SSgA moderate strateq, and SSgA aggressive. Any input would be awesome! My managers say to put it all into publix stock, but obviously that's not the best idea. If they went belly up i'd be out of a job and my savings.