How can I preserve hair or saliva for future genome sequencing?
Full genome sequencing is only one of many experimental approaches. It's important in the field of genomics and useful in transcriptomics and proteomics.

It's best to extract DNA as soon as the sample has been removed from the living organism since all kinds of physiological processes start breaking down DNA in dead tissue. Kitchen refrigerators are not ideal for storing extracted DNA because they operate at about four degrees celsius. In the lab, minus eighty degree freezers are used. The lower the temperature, the better. Minus eighty degrees, however, is good enough.

Contamination is a big problem, so the more technical repeats you run, and the more biological repeats you have, the better your chances of getting reliable results. Biological repeats refer to, for example, taking three strands of your hair for analysis, while technical repeats refer to, for example, carrying out three PCR experiments on material from the same strand of hair. Once you've used tissue to extract DNA you don't keep remaining tissue because it gets contaminated during experimental preparation. That is why you may want to have biological repeats. It's also important to take precaution when removing the sample from the organism. This means wearing latex gloves and even using dilute ethanol to sterilize the sample before placing it in a sterile container. The problem is that ethanol can interfere with DNA extraction and be a contaminant itself. Balancing contamination prevention with quality results is important in the lab.

There are additional biological information such as DNA methylation events that occur intermittently on a genome and are inheritable. This information cannot be predicted from the sequence composition of your genome, but there are experiments meant for elucidating methylation patterns that can be carried out using uncontaminated biological samples (such as hair and saliva) stored in eppendorf tubes at minus eighty degrees celsius.