Several of the SAR reports note that victims were able to get a 911 call through. However, cell reception is VERY difficult to get. [1] [2]

cell tower location

• many websites offer data; it originates from the FCC database
• one of the better ways I've found to explore the data is this Google Earth data source

• 1254295 near Packwood, WA US Cellular
• 1064744 inside Packwood, WA multi-tenant
• 1064743 between Packwood and Randle multi-tenant

how to build a parabolic reflector

• kunkel @ umass.edu
• Tool Using Animal @ Instructables
• solarcooking.org
• four-layer design @mit.edu (pattern on page 15)
• general-purpose calculator @ making-photo-gear.com
  One of these sewn out of conductive fabric would probably fare well in a backpack, since the only thing that's rigid are the poles. However, this would require a little effort to sew.