There's an intentional tool for @ $5 with a carbide tip that should be available at home-center type places, but for a small job you could sharpen one corner of an old screwdriver, use a scratch awl, anything steel you can get accuracy with along a board straightedge.

For holes, a holesaw drillbit mandrel with changeable hole-thangs in different sizes, also available at the amateur level. Cometa think of it, pick up an amateur level while you're there...