Depends on how wealthy your family are - but for landsacpes I would consider the below a good start:
£0 - £50
Hotshoe Spirit Level (best gadget for under £10)
White Balance Filter e.g. Expo Disc
Sun Position Compass - ID where the sun will set / rise at any time of the year.
DoF Calculator
£50 - £100
A nifty fifty (50mm f1.8)
Sensor Cleaning Kit
£100 - £200
Manfrotto 190XProB Tripod + basic ball & socket head
Lee Filter digital starter set (ND and ND grad with holder, case and cloth) - £175ish (best filters for Landscapes)
£200 - £300
Sigma 10-20mm - one of the best value wide angles available
Sigma 18-50mm f2.8 - nice upgrade from your kit lens