Speaking for myself , I've never owned a core drill never felt the need . I hired them a very few times when I was lumbered with drilling holes for fans , I wouldn't bother if I were you Bob.
A cable spooler like below , mine's home made but you can buy them .
A length of flat steel about a foot long X 25mm wide X 1/8" for bashing down behind skirting boards on existing houses.
A selection of Flat drill bits ..20mm , 25mm .
But the first thing to buy is some KNEEPADS!!!!
Edit : Just thought of a few more things .
A length of lid from mini trunking YT1 or YT2 is excellent for widdling under floors etc ..tape cable to end .
To fish across a suspended ceiling etc ...20mm PVC conduit ..couplers but no glue... and an end (Terminal) box on the end . Twist so the end box is upright and it willl often lift over T bars , joists etc.
My mate has an excellent circular saw, small blade ...bit like an angle grinder, can be set to cut floorboards , bought in Lidel , German brand , not rubbish . Well worth the money .