etiquette modification

you know, there are a few things that i'd love to see some etiquette created around (or removed from):

1 - being at a restaurant and eating the food that other people aren't going to finish
if you see somebody giving back a half-eaten plate of food, and the person looks half way normal, and the food looks at least half way delectable, what's so wrong with asking if you can finish it rather than having the restaurant throw it away? i hate that this is frowned upon. of course i can imagine it being taken too far, with strangers beginning to lean over, stick their noses in your plate and ask..."you gonna eat that?" but if the etiquette is created properly, this scenario will be avoided entirely.

2 - helping blind people walking down the street or in the subway
always want to help -- i mean, i can see, they can't -- but never know whether it's appropriate. why isn't there a universally agreed upon etiquette for this?

3 - telling girls their thongs are showing
among the sistas, this should be allowed. i am not a female empowerment person, but having your thong show is somewhat embarrassing for obvious reasons, and i'd just be more comfortable if the etiquette were only among girls. this could extend to the other gender in the form of telling people they have something in their teeth, etc...

4 - saying "bless you"
totally stupid. remove it entirely.