You can't substitute a good old fashioned spare wheel but fitting them on the roadside can sometimes be problematic and dangerous.
I use Slime which is a tyre sealant and put it in all my tyres (Cars, Bikes, Campervan) and have never had a puncture since (we're talking in over 10 years on some of the vehicles).
Its a preventative and works absolutely fine and is safe but wouldn't work if you took a huge chunk out of the tyre.
If it was me I would use both, Slime and have a spare in the boot just in case