So Ive played with some guys recently and i might be close to doing some small performances with them soon…barrooms and pub basements. Thing is… i have no idea how my bass will be set up in the sense of the signal from my bass getting to the audience and what that actually looks like; do they mic amps? Will i be plugging into a mixer/pa?
Right now i have my bass straight into my little 20w practice amp but i can get my hands on a 40 or 100w combo amp.
If it goes into a pa/ mixer will i need something to boost my signal before like a pre amp or amp head?
In addition i have come upon a cheap compressor & overdrive that ive had fun messing with, other than that not much else.
And going forward, what are “the basics” i should consider aquiring to be ready for future shows? Tuner pedal, power supply, etc.
Tuner pedal is always a great thing to have. Peterson StroboStomp is fantastic.
Not that i’ve ever had a gig, but my (uneducated) guess is you’d need a balanced signal for that. Might want to look up what uses a DI box has.
Spare strings, and if your bass needs it, a battery or two 
If your amp has a direct line out that can be used to connect it to the FOH PA. Both the Rumble 40 and Rumble 100 have one. Check out a pic of the back panel. You’ll see it below the input jack for the footswitch. Lacking that feature the sound man will need to use an outboard direct box.
I would not even attempt to use a Rumble 40 at a gig unless it was one where everyone was playing very quietly and without drums. Even the 100w version is barely adequate for a full on band gig w/drums. You won’t have a whole lot of clean headroom before you begin to get some distortion at higher gain settings. But if you’re depending on a PA to carry the room the 100w is adequate for a personal stage monitor.
Too adequately carry even a fairly small room with just your amp you’ll need 250-300w minimum and an efficient speaker. Preferably a single 15" or 2x10". 500w would be better. Bass requires an awful lot more power than a guitar to handle the lower frequencies cleanly and clearly.
If you plan on running a pedal board with a tuner and a compressor you’ll need 9v power supply. If you’re playing a passive bass I would use the overdrive set to it’s lowest gain level and use it as a clean boost. That can add a bit more gain and volume the amp sees as a result of the boosted signal.
If you bass is active may may not need it. Just depends on the pickups. Spare 9v batteries for you active bass, comfortable strap, some picks and a very good quality instrument cable. They don’t need to be costly either. I use MXR low capacitance cables. They run $20-$30 and offer great quality. A 15’ cable should suffice. 20’ max but the shorter the better. Happy gigging.
You need to talk with your sound man ASAP. He’ll answer all your ?'s about how you’re gonna do this. I have a tuner pedal and that’s it.
I think you’d be better off asking directly your colleagues what kind of show they might be planning/aiming towards. If they are also new to this experience, talk - all of you - well in advance with the responsible/sound guy of your first gig and prepare accordingly…
You might need everything, or nothing. And exactly the opposite for the next gig, of course 
I’ll say we played a restaurant/pub Friday night full drum kit 20w guitar amp and my Rumble 40. My bass volume didn’t even make it to 3 o clock and we were too loud for the place.
We did our best to keep it down, drummer still played with real sticks and all and after soundcheck we were able to get a good sound going.
I didn’t have any faith in my Rumble but I was surprised. Would it have worked on a big stage and an open room? Maybe not but I’m pretty sure I could have gotten away with a 25w bass amp for that show.
I have a 100w 12" that can extend with another speaker to 160w I think that’s going to be my go to for a bigger room.
We are just a cover band not a metal band so moderate volume was fine for us.
We actually got thanked by the owner for, “sounding great and not blowing the place out like some of the other bands”
Congrats on a successful gig!
Even @JoshFossgreen rated the Rumble 40 as the best beginner amp. I’m on my second. I had to sell my Rumble 40 before moving from the U.S. to France (it didn’t support 230 VAC). I bought a Studio 40 once my basses showed up after the boat trip from L.A. to Rotterdam. I wasn’t necessarily interested in all of the presets, but more interested in the FX loop and Pre- and Post- DI outputs. Plus, it has a black grill cloth instead of gray, which I prefer. I stacked it on my GR Bass AT Cube 500 combo until I managed to find its matching 112 cab. Now it’s in the living room for playing along with videos on my 65" TV.
The Rumble 40 is a pretty efficient little amp. I’m not surprised it could handle a low volume gig in a smaller room even with drums. I’ve rehearsed with similar 50w and 75w amps with a full band and still been able to be heard just fine.
But I wouldn’t depend on one to cover gigs where the needs were much greater than that. It’s why you have your more powerful 100w-160w rig. I’m confident my Genzler MG350 combo could cover a whole lot of gigs in smaller rooms but I’m also adding a second cab to run at 350w for when I need more volume and headroom.
My advice to anyone playing gigs or rehearsing with a full band is that it never hurts to have more power and speaker area than needed, only too little. Every amp has a master volume control so we can always turn down but within limits we can only turn up to that limit and it’s never good to have a need to do so.