If the main page of my site has a meta tag containing all the keywords of my products, what should I do for the misc sections of my site, such as contact page or sitemap?
Don't use all keywords in home page . (main page as you mention). Better create landing pages for your products or product category. Landing pages help you lot, Because it is easy to optimized and PPC.
For the main page I would just focus on meta tags for the actual home page and not the rest of the site. But, SE's dont use meta tags too much so I wouldnt put too much effort in to it.
You can use your targeted keywords on your home page, and at the same time you must have your targeted keywords on your specific targeted sub pages, to synchronized your Landing Page...
Google adding the Description Meta Tag won't result in a boost in the Search Engine Results Pages (SERPs), but the description might be used for the description for your SERP listings in Google. Yahoo says they use the Keyword Meta Tag when it ranks a page. So it makes sense to add one for Yahoo and any other minor search engines that still use. There are few important tips for good meta description tags: · You should Used keywords in your meta description tag. · Don't repeat the words overly often, but try to use multiple syntax of your keywords. · There should not be more than 150 characters in a description meta tag of a single web page. · Use a different meta description tag for each page, as each page is different.
don't use all keywords for home page rather devide all keywords efficiently among all your site. One more thing : It is not required that you use all keywords that u needed rankings for, rather use all other combination also. You can take an example of my site "Professional seo company", check its meta tags. We have use many other combination also for which we are not expecting rankings with the combination of keywords.
For Home Page- Use the main first targeted keyword in metas and few other priority keywords as well. For Sub Products Pages- Use the products related keywords, secondary targeted keywords For Misc Pages- Use a common pattern like Page Name - Main Product - Brand Name (for example - Sitemap - Mobile Phones- ABC Mobile Phone Shop)