Joe,
no need to buy spares before they break, JMHO!
Luger.parabellum's suggestions are good, but there are only one or two "serious" luger armorers in the US. most 'smiths don't know squat about lugers.
For shooting Winchester White box is good. As is Fiocchi, S&B, and mag tech- all non +p, and in 115 or 124 gr FMJ. I've used the all with good results.
Many/most folks here worry too much about breaking a luger part. As long as your pistol is not a rare all matching historic one, and yours is a good potential shooter, just shoot it!
What ever spares you buy will not be the ones that break: Murphy's law in action.
If your grips are matching and fit well, they should not be a problem, if loose yes.
There are cheap replacement grips available on ebay and I personally prefer the post WWii German VoPo plastic grips, they can be had for $40 a set if you look hard.
A Mec-gar mag is a good investment, always good to have two mags, or more.