Education.com has some really nice math activities for all grades, especially for high school students. Although there are only 13 activities, I already found one that would make a fine geometry activity and could be used in several places in the geometry class.
The original suggestion is for a geometry scavenger hunt. The idea is that you prepare a list of geometry terms for the participants. Make sure they all understand the terms and then send them out to take photo's of objects representing the terms. It is suggested the pictures be downloaded and shown so everyone can agree if the photos do contain the terms.
Why not send the students out to take photos as a homework assignment, download or share the photos to a program which would allow them to annotate so they identify the part of the photo that meets the term by circling the object and writing an explanation of why it meets the definition of a term. In other words, defend their choice through writing. This shows a more indepth understanding of the term.
Another application of this same scavenger hunt idea is to send students out to take pictures of whatever interests them. When they come back they download the photos to their annotation program and they can identify the slope of each parts of the item. For instance, the picture to the left has all four slopes in it. By identifying the slopes, I make more of a connection.
I could also look for examples of shapes such as rectangles, triangles, etc. I could even look specifically for triangles and then classify them by side or by angle or by both and turn it into a presentation.
Then there is the activity to find the best priced pizza in town using price and diameter. Even if you don't have a pizza place near you, this can still be used in class. I live in a place where the closest pizza place is about 140 miles away but we can buy frozen pizzas in town. So I send students working in pairs out with their mobile devices and a ruler so they can find out the diameter of the frozen pizza's at the two small stores in town. They can actually just snap a photo of the pizza with the ruler showing the radius or diameter. Once they get back, I can have students use this activity to figure out which pizza is the best buy.
The last activity I looked at would be appropriate at this time of year or anytime you have a bag of miniatures. Students record the name of the candy, the weight and the calories in a data chart for the different types of candies in the bag. Once done, they create a bar graph based on calories for each type of candy. I would have students add a written report discussing if the candies all weighed the same and if they didn't was this comparison reasonable. I might even have them calculate the weight per gram.