If you're typing up or scanning notes, make sure to back up your files. In addition to using an external hard drive, any of these free tools can help.
Live Fieldnoting - Tricia Wang describes this method of taking fieldnotes using a combination of social media: "a live fieldnote is a blog post that is intended to provide an on-location and synchronous visual and textual coverage of an instance from the ethnographer’s fieldwork. The live fieldnote is created with a image sharing app on a mobile phone that is then shared to other social networking services. Images are accompanied by a description of the image and can also include a brief analysis of what the interaction means to the participants in the image and/or to the ethnographer. All live fieldnotes are timestamped, publicly accessible on the internet, and include location data. Live fieldnotes demonstrates the combination of two activities that are central to ethnographic research, 1.) the ethnographer’s participation in a social world and 2.) the ethnographer’s written account of the world through her/his participation."
Keep in mind: Intellectual property -- for example, who "owns" the media you share on Instagram?
Smartpens - Smartpens allow you to take notes while simultaneously recording spoken audio (interviews, lectures, etc.). By using special paper in conjunction with the pens, you can tap any point in your notes and the pen will play back what was recorded at the corresponding time. The pen also saves digital copies of your notes, which may be transferred to a computer via USB. The most popular smartpen is the Livescribe, which can cost between $150-200.
Keep in mind: cost, access to supplies, battery charging requirements, bulk of pen.