Search around, this topic has been discussed to death lol. For your convenience I'd recommend a day light loader Watson-type,.
I find Leica IXMOO much easier to load and more secure than spent cassettes. Obviously it can only be used with Leica, find generic metal ones on the bay for other cameras.
If you do it carefully you will never scratch or expose it, I scratch one in like ~50 rolls and it's not that bad so it's safe.
Bodies: Leica IIIf - Leica M3 SS - M6 Classic - M6 Black TTL - M8 - VC Bessa R2M
Lens: VC Skopar 21/4 II - VC Skopar 35/2.5 - Summar 50/2 - Summicron DR 50/2 - Elmar 50/3.5 pre-war uncoated - Summarit 50/1.5 - Summitar 50/2 - VC Heliar 50/2 - Nikkor S.C 50/1.4 - Canon LTM 50/1.2 - Nikkor P.C 85/2