We all carried 6 to 8 mags, 28 rounds each. Wierdly I have never checked to see if that was an old wives tale. We also carried a full bandolleer or two, I think they had 5 or six sets of 30 each. Just in case things got ridiculous.
There would also generally be one man with a pack full. Though it's not about carrying, I also habitually rotated mags. Still do. Every couple days, unload all mags and use your other set, then clean each round and magazine. I find the process extremely thereputic.