01) If I get a step up converter to allow me to run UK 220v equipment on 120v, is this also OK for 110v?
02) Can you use standard 230v equipment on 220v grid with out a converter?
03) Is there a piece of travel kit that can cope with different voltages?
1 - Yes it should be OK. The voltage in most countries varies slightly. The convertor however could be a heavy (weight) transformer depends on the current you want it to deliver.
2 - Yes, if it was an AC motor it would run marginally slower, so a razor would be OK
3 - Some things run on various voltages. For instance the charger for my mobile will run on 100 - 240 volts AC / 50 - 60 Hz. check out the equipment, it is usually printed onit.
The market is full of kit that will run on 12 volts DC or can be recharged - off the bike system.
.. no gods .. precious few heroes ...