That means you have to prioritise, and plan ahead. The one bag, in the first instance, is going to have to be your guitar case. The massive pedal board may seem important, but let's be honest - no-one really knows the difference between 'fuzz,' 'overdrive,' and 'distortion.' There's probably going to be pretty serviceable reverb on the amp when you get there, and nobody, nobody wants to hear 'flange.' All you need to do is stick your delay in one pocket - get that small one by Boss and stop your whining - and shove just the one fuzzy sort of overdrive pedal in your guitar case. The guitar is the main thing - arrive without the guitar and you will find that you don't look so cool when you walk out of the airport. Merch is more tricky. Apart from the bit where you get to walk out of the airport looking cool with a guitar case, there's not a lot of point in going on tour unless you're going to sell merch. Now, it won't fit in your guitar case, so what you'll need to do is fill your hand luggage with CDs or vinyls or commemorative dolls or whatever the kids are buying these days at their concerts, and carry the whole thing on board looking all nonchalant like 27 kilos ain't even a thing.
That pretty much takes care of the checked baggage and most of the hand luggage, especially if you're like me and insist on taking your violin everywhere (that's kind of a looking cool thing as well - nothing says 'I may not have a job but at least I can complain about suffering for my art while you buy me a drink' like a battered old violin case). That means you really don't have much room left, so you're not going to be able to bring anything to keep the rhythm section busy. Which means honestly I think they shouldn't come because they'll just act up and it will be a headache.
The upshot of this is that not only is there no room for the rhythm section, which is not in itself a bad thing, but there is also no room in the modern musician's touring kit for a spare pair of socks. Or, say, a clean shirt. Sometimes you even have to only bring one cape, which can be a hard decision. You see where I'm going with this, of course. A few nights of the devil's music, no change of socks and whoops I forgot my toothbrush, and it's no wonder if that musician in your life smells a bit like teen spirit.