What you describe has nothing to do with billable time, so I certainly would not endorse the concept. Even if you could call up inventory and non-inventory items, what would the program do with them? A billable time entry is neither a sales invoice nor a receipt. So there they would sit.
Travel distance entries are best handled as expense claims, if you are reimbursing employees for them, because they are an implied expense. Of course, if the distance charges are for company vehicles, they would just be non-inventory items.
That said, there is already an idea that would cover your request: Billable Services tab. Look only at posts #1 - #7 in that topic. Post #8 diverted the discussion down a rabbit hole that two moderators tried without much success to correct. Ultimately, that part of the discussion was made irrelevant in December 2019 when Manager’s accounting for billable expenses changed.