Removing DNA from cheek epithelials works reeally well and is quick and cheap to carry out. You might be pushed to stretch it out to 2 and a half hours. TLC of chlorophyll is also fun and works well. Grams staining bacteria is also fun and easy to carry out. As is immobilizing algal chloroplasts and using them in photosynthesis experiments. Heaps of exciting stuff to do in Biology!