Final answer:
In the given context, 'tomes' refers to large books that Bobby finds cumbersome to carry to class, suggesting their considerable size and weight.
Step-by-step explanation:
Based on the context clues in the sentence provided, the word "tomes" most likely refers to large books. Bobby mentions that his backpack is bulging and heavy as he transports these items to class, which suggests that they are of substantial size and weight, typically characteristics of large, heavy books. Thus, in the given context, "tomes" is synonymous with large, voluminous, or extensive books, often implying a degree of formality or scholarship associated with the content.