Side-by-side I saw

• "The C programming Language" (1978)
• "HP 3000 Computer Systems MPE software pocket guide" (1981)
• the two volumes of "System V Interface definition" (1986) (fallen apart from how often it was used)
• "MC68020 32bit Microprocessor User's Manual" (1984)
• "Uniplex II plus" (1986)
• "ANS-Cobol" (1974)
• "The Unix System" (1983) by Bourne

IIRC there must be a three-volume set of nice blue bound books with the System III manual