I've developed a much thicker skin as it's like running the gauntlet round here sometimes with charity collectors, chuggers (who get paid for it), Big Issue sellers, beggars etc...
I give to who I want to give to and would rather give more to them than less as I've felt guilt tripped into giving to others.
I don't go to large supermarkets very often so don't come across many bag packers so, if it's a decent charity I will give them some money though often need to repack my bags a bit after though, at least they are making an effort though.