A good friend of mine told me years ago that the best time to visit some of the museums in our area was during the first week the public schools are in session. I have taken her advice often and it has always been great. Yesterday, I took my kids to the local Science Center and we only had to share it with about 3 other small families.
While planning your field trips this year, look to schedule them in the early afternoon. If a school does have a field trip to that particular place, they will be leaving shortly after lunch time in order for their students to catch the bus and you and your children will have the place to yourselves. Also, schools rarely plan field trips for Mondays. When you don't have to share a place of interest with 300 other school children, guides will have more time to talk with you and answer questions and your children will be able to handle any hands-on displays without being rushed.
Just some helpful homeschool hints!