Do you and your students have access to computers? I use an excellent website: www.cellsalive.com
Kids can click on cell parts and see a thorough description of the cell part and its function. I usually have my students make sketches with labels and take notes as the explore the website. There are lots of ideas for making plant cell models in ziploc bags (baggie represents the cell wall) and jello (to represent cytoplasm), grapes, etc (to represent organelles). I'm sure someone here on ProTeacher will post the instructions.
Sorry I can't help more, but I go back and forth between 4th and 5th (cells are a 5th grade topic)
so it's difficult to remember details about specific activities.