I am thinking about doing the mason jar glasses as favors and allowing the guests to use those to drink out of. Do I order enough favors for everyone that I invited (175), just the estimated number of guests (100), or wait for RSVPs? I was thinking about just ordering the estimated number, plus some extra. I don't want to be left with 30 mason glass jars afterwards.
We actually may not even do favors, but if we do, this is our idea!
Re: How many favors do I order?
Do you need to provide your own drinking glasses at your reception? If no, use what is provided or get the mason jar glasses if you really like the look, but I don't think you should make used glasses your favor. They will be sticky and dirty from being used and people won't want to put that in their cars and take them home and then have to wash it. Plus people will prefer something edible if you do a favor; many do not like to take one random, mismatched glass home.
If you do need to buy drinking glasses you will need a lot. You might have some luck trying to sell them after your wedding instead of giving them away. If you want to try to give them away, there is no harm in putting up a sign that says people can take them home. I went to a wedding that had a table with the lids and a sign that said to take it home. I left it there. I didn't really consider it a favor and it wasn't something I wanted.
Of course, as you mentioned favors are optional so you don't need to do anything if you don't want to.