I did one run. I got an item. 100% drop rate.

With a sample of less than 100 you are wasting your time trying to compute statistics.
With a sample of at least 1000 you can start to establish a trend. This also is not too hard. 100 runs with 8 people is 800 samples already.

Now, for some super sloppy maths: Generally every run i'm in everyone says what they've gotten. Typically someone gets a weapon every 2-3 runs. And someone gets a totem/nut every 2 runs. Therefore you could speculate the figures are around:
1/16 for totem (6% drop rate)
1/24 for weapon (4% drop rate).

Therefore, if we want to keep numbers easy, on average it would not be unusual to see a 5% drop rate for a weapon to fall (no guranatees on duplicates. You can see my better-maths post on that).

Does this mean: I run 20 times, I get a weapon?
No.
Does this mean: I run 100 times, I get a weapon?
No.
Does this mean: If I watch what the drop rate over 10,000 runs will I see a trend of approximately 5% being observed, plus or minus a few percentage points.
Yes.

Probability... you have to love it. I know casinos do.