This is exactly why sensible companies have discretionary budgets at every level, ideally including individual employees. Below a certain threshold, it costs more to review than to just trust that people are asking for a reason; as long as there are controls and records in place to catch potential abuse or mistakes (e.g. paying for the same thing multiple times), approval requirements should be proportional to amount. On the off chance someone is being frivolous, it's still not worth imposing painful review processes on everyone.

An individual employee at a technical company should be able to spend $100-200/year with discretion (mouse, keyboard, utility program, cheap service, etc). (That's not counting whatever the company might allocate for people to get their own development systems, which some companies do.) A first-line manager should be able to approve more than that (e.g. a monitor, a more substantive service).