The second part of your question concerns Huck's own spirituality. He is agnostic, meaning he doesn't know if there is or isn't a god; for him praying just doesn't connect him in any way. But the really important part here is that Huck doesn't try to foist his views on others. If it works for them, fine. Unlike others he encounters, Huck does not try to press faith or prayer on anyone.
The search party filled the bread filled with mercury in the hopes that it would be attracted to his "dead" body, so Huck scoops one up.