A few suggestions:
-Receiving blankets. You can never have too many as they can double as burp cloths.
-6-12 month size clothes for baby; this is always my mum's go-to. Babies grow so quickly and so those clothes will come in handy very soon! Just ensure, of course, that trousers snap up the crotch (for ease of changing nappies), tops have snaps on the shoulder (for ease of getting over baby's head), and there isn't too much lace or too many frillies on the clothes (babies often don't like them).
-If you're crafty, you might consider making something special for the baby. Birth records and cross-stitched baby quilts are what I usually give. Cross stitch isn't hard to learn, and birth records are usually fairly simple projects. Cross-stitched baby quilts usually come with the quilt pre-made; it just needs to have the design stitched. You can also cross stitch or embroider baby bibs.