Carrying ramps is not really a viable solution.
Even lightweight portable ramps are quite heavy, they have to be to take the weight of a powerchair, (my wife's is a small chair and weighs 125kg).
The height that you need to rise affects the length of the ramp required.
To rise two steps will need twice the length of ramp as rising one step and even that would need to be at least 1200mm long, it wont be easy to find/carry/store a ramp that's 2400mm long.
If this is to access a shop, it is the responsibility of the shop owner to make it accessible, a metal ramp could also cause damage to the cill of the doorframe: your ramp, and you'll be liable for the damage.