>>> Do strikers get paid?
No. Some unions may have strike funds though, which can provide a very basic allowance to strikers who need money for basic essentials.
>>> Can they claim any kind of benefit?
In general, no. However I'm not sure whether Iain Duncan Smith's 2012 plan to block Working Tax Credits to some (very low paid) strikers was ever brought into effect.
https://www.theguardian.com/society/2012/jun/17/workers-strike-lose-benefits
>>> Can they use holidays as strike days or call in sick?
I have little doubt that some employees, who don't want to be seen by their colleagues as strike-breaking (but who don't want to lose any pay), will book paid holidays which just happen to coincide with strike days. However it's not meant to work like that.
Equally, I'm sure that some employees will tell their boss "I wasn't going to join the strike, so I'd have been at work if it wasn't for this terrible tummy bug that I've just picked up" - but that won't help them anyway unless their employer provides sick pay (which many don't). Once again though, that's not what's meant to happen.