Actually funnily enough there have been two times during my training so far where i've thought i had a radio failure only to realise that on one occasion i'd caught the headset lead on my kneeboard and pulled it out, and on the other i had the volume on my headset all the way down. The last one actually being on my solo check out. The instructor/examiner made all the radio calls for me, so i had an easy time!
With regards to light signals and flares, would all controlled airfields carry flares etc? I've never seen it happen so i'm not sure i'd know where to look for the light signals (obviously at the tower, but are they noticable/easy to see?). Do you think ATC would be open to me requesting a pretend radio failure circuit?