In nonfiction is it a good idea to capitalize nouns that precede numbers or letters, as in: Refer to Table 1. He presented Exhibit A. It happened in Chapter 4. He stole cash from Register 2. I liked him since Day 1. That is illustrated in Appendix B. If this is good, should we cap the plurals too? Refer to Tables 1 and 2. He presented Exhibits A and C. It happened in Chapters 4 and 5. He stole cash from Registers 2 and 6. That is illustrated in Appendixes B and C. Thanks.
Here's an explanation about capitalization from the Blue Book of Grammar and Punctuation (link). Not to dismiss your question here--keep posting!--but you seem to have a lot of questions that this book could help you with.
It depends on context. In academic papers, words like "table" and "figure" are capitalized when preceding a number (e.g., "Refer to Table 2."). In your examples, "register" and "day" would not be capitalized because they aren't functioning as proper nouns. I feel like "exhibit" could go either way; again, it depends on context.