Weight limits vary between airlines. Normal allowance is a carry on and a personal item.
Ryan Air has a 10 kg, single carry on limit. I handle this by carrying minimum equipment in a Gura Gear Kiboko bag, weighting just 2.2 kg.
The bag contains 2 DSLRs, Ultra Wide, 24-70/2.8, 16-80/3.5-4.5 (APS-C), 70-400 4/5.6 and a Arca Swiss D4 tropod head. MacBook goes into pockets of a Domke west. Oddball lenses go into a heavy duty case to be checked in.