Tyres & tube
If you intend on road cycling, put on road tyres called "slicks", which make the ride less exhausting. Using grooved tyres you waste about 10 % of your energy. Road tyres should be fully inflated, especially the rear one since it carries most of the load. Do not overinflate them, though, because when pressed against the rim, they may deform and later explode.
However, if you plan to cycle off-road as well, semi-slick tyres are the better choice. They have minimal tread in the middle and deep tread on the sides.

If you plan to have a fair amount of luggage, the tyres should be of good quality. Do not use ultra light tyres, as they are not durable enough.
Make sure that rubber inner tubes are of proper thickness - they will be more puncture resistant.