ebay...

search for something cheap 2nd hand like small compact handbag sized Alesis nano piano module

http://www.harmony-central.com/Synth/Data/Alesis/NanoPiano-rev.html

get a decent pair of small powered [built in amp]computer speakers..


and a good quality budget price midi control keyboard

[more expensive ones have 88 weighted keys]

which you can play on your lap..
[no more noticable than a dulcimer..!!]


then as long as you can find a spair electric socket in any club
within reach of an extension lead..


this whole kit would fit in a sports bag and be nowhere near as visually obtrusive as your portable keyboard,
if you place the module and speakers safely out of sight under your chair..