Slipping plectrum

[fatt-dad]

get some violin rosin. Make a bit of dust. Drag your index and thumb on the dust where the finger touches the pick.

No more problems!

f-d

[belbein]

I use the Beagle method.

I accidently drop my pick on the floor and forget about it. My beagle finds it and chews it up, always on the wide end. Instant traction. They never slip out of my fingers.

My beagle is available for custom jobs.

[Paul Kotapish]

I've been fighting pick-slippage for 55 years and I'm finally getting the hang of it.

I really like this Dunlop Primetone 1.4 with the "grip" surface. Nice, fat tone, a bit of point for clarity, and a textured surface to eliminate slip.

[Steve Ostrander]

I’ve found that different plastics have different levels of tackiness. I use sandpaper on my Dunlop Ultrex. On Rhinos I take an Xacto knife and crosshatch them. Then I have Cool Picks that work well with no retouching.

Another trick is to glue sandpaper to the pick. I’ve heard of others putting bow rosin on their fingers. You just have to experiment and find what works for you.

[Simon DS]

Everyone goes through this. I don't think the solution is special equipment. The most common reason for this is gripping too tightly (I know - counterintuitive). Try to relax your grip (if you are squeezing) and make sure the attack angle of your pick isn't parallel to the strings.

Yes for me it's a bit like this.
Damp your fingers. Now imagine holding an invisible pick tightly between thumb and finger. Muscles tight and wrist loose. Now there's a gap, right? You squeeze the pick into that gap. With a loose left hand prevent the strings from ringing and strum for an hour (!) I'd have pick parallel to strings and make sure the pick doesn't bite into the strings too deep. Let the pick sort of drag a bit.
Good luck!