If I had to choose one book to carry with me on a research trip, it would be Judy Jacobson's Field Guide for Genealogy (Baltimore, Md.: Clearfield. Co., 2nd ed., 2003).I must confess, I love nature field guides for their portability and breadth of information. The Field Guide meets these requirements, and makes for good reading as well.
This is largely a book of listsof household goods found in estate inventories (ever wonder what an "open betty" was?), diseases and epidemics, unusual nicknames and odd given names (who would name their child "Avoid Illness?"). Jacobson gives advice on finding and using sources, tips for deciphering old handwriting, and descriptions of antique clothing and hairstyles that might help you date the tintypes in your attic. In no case is the information given exhaustive, but Jacobson offers at the end of each section "Topic Sources and Additional Readings."
The highest compliment I can pay Jacobson's Field Guide is this: It is the only genealogy book I have found worth keeping in the glove compartment.