The hardest gift to buy for someone with a well-used workshop is a new tool. They probably already own the one you'd choose, and they often prefer a particular brand or model. Accessories, consumables and spare parts are nearly always a safer choice.
For someone with brushed power tools, a spare pair of carbon brushes for each of their main tools is a gift they will use. Find them by brand: Makita, DeWalt, Bosch and Hitachi and HiKOKI. The tricky part is knowing which tools they have, so check the model numbers first.
Cutting consumables are an equally safe choice: a mitre saw blade, a pack of cutting discs, an impact-rated screwdriver bit set or a cobalt drill set in the common sizes. See cutting tools and drill and screwdriver bits. For woodwork, a set of router bits opens up new jobs: see router bits and parts.
Hand tools that people rarely buy for themselves also go down well, such as a ratcheting pipe cutter or a basin spanner for the under-sink jobs nobody enjoys. Browse plumbing tools and engineering and workshop tools.
For someone who has just started a workshop, a starter set of consumables works well: backing pads, abrasives, a pack of blades, a pair of brushes for their main tool and a small box of fixings. See sanding pads, screws and fixings, and the tool parts hub for everything else.