I agree with the others, do what you want to do and don't worry what others aren't doing. Also martyrs have no value in a PTO. We had a couple some years back at it just decimated the moral of the group. Don't point fingers at others, just do what you do, if she is that bad it will start showing, when you refuse to pick up her slack. Good luck.

I think you should do as much as you feel is fair for you to do and then stop. There should be no martyrs in a PTO and your frustrations will hurt rather than help the organization you serve. If you want lunch - take it, and they will have to find someone else to do the work. If however, you decide to do things--do them with a happy spirit and look beyond what other are not doing. It will be your greatest gift to your group.
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Do you want to be President next year? You have to speak up and let people know. Some people are afraid to speak up. It sounds like this is you.

As for the president, ask her to help, and if she runs off, go with her or leave. It shouldn't take long for her to figure out that things aren't getting done when this happens. When Lunch time comes, go eat. If you want to come back then do so. You have the right to make it clear that you can work until lunchtime, then you are leaving. You are a volunteer. Maybe you need to tell the president the jobs you have left for her to do. Be direct. You need to go do this or go do that.

As for the other volunteeer, When she isn't there, talk about if she comes how you'll give her part of the same job if she comes. You need to be asssertive to tell her the part of the same job you are doing that you saved for her. Maybe you can figure out how some of the jobs can be arranged for her to come and help, but still feel needed.

I am currently a Volunteer in my child's elementary school. My problem is the PTO President is very lazy. She does a great job delegating work but when it comes down to it, she makes up excuses to get out of doing the hard work and leaves only myself and another volunteer, doing the work she delegates. While I don't mind doing my share of the work, I would like to know if it's ok for her to run off and "visit" with teachers and other parents instead of helping out. Also there's another "volunteer" whom has agreed to be PTO President next school year. This woman is hardly around because she goes to school. My complaint about her is when the other volunteer and myself are doing a job delegated to us, she comes in and trys to take over and literally bosses us around. When she does this, our work is messed up and it takes that much longer to get the job done. We don't want to hurt her feelings, she's a hard worker, but the other volunteer and I work as a team because we usually don't have any help. We have given her other jobs to do but she refuses to do them and wants to do what we are doing. The PTO President encourages this also. What can we do?? We get frustrated because we sometimes have to skip lunch in order to get the job done, since it's usually only two of us and the PTO President takes all the credit.