rxmd
May contain traces of nut
It's not a huge issue but lead bags will do exactly nothing to help. Cosmic rays are energetic enough to go through a lead bag like it's tissue paper. That's why Kodak (sigh) store their master film rolls in caves miles beneath-ground.
This is a discussion that while technically true is also completely irrelevant.
Cosmic rays are sparse enough at ground level that as a camera owner you really don't have to bother. You're more likely to lose your camera from dropping it, getting it stolen etc. than from the sensor becoming unusable due to excessive hot pixels from cosmic rays.