The equipment will depend on the mission. In particular, the length of the mission, the size of the crew, the total weight of the ship, and very strongly on the exact nature of what they are going to be doing.
Imagine a mission that is intended to be almost entirely observational. Go out to Jupiter, for example, and carefully look around. No landing on anything. No obtaining physical samples. The equipment for this is likely to be oriented towards keeping electronics and optics working. So they would have lots of equipment for that. Such a mission might be quite limited in mass. They might consider that, if they needed a huge industrial arc welder, they are probably already dead. Because they might think the only thing they could want to weld would be the ship's hull.
Turn it up a notch to landing on one or more of the Jovian moons and collect samples. Now you have physical equipment that may need to be patched up. Or adjusted due to last-second changes in schedule and plans. Oh, we can't possibly use this equipment module because the chemicals we have detected, from orbit, would utterly prevent its operation on this moon. So having it in the lander is a complete waste. Let's get it out of there fast so we can complete the mission. An arc welder might be the required tool. Or not, I'm not any kind of mechanic. But a lander could easily have a minor accident like bending a landing strut or scraping something. Or some equipment gets caught in a small little shift of rock. In the hands of a skilled tech an arc welder can do lots of cool things.
Turn it up yet another notch. It's a colonization mission. In this case, you would have many hard to predict tasks. Fix this, patch that, build the other. I once watched my uncle deal with a nut that had been "painted on" to a bolt. He got his arc welder and just sort of flicked it over the paint. The paint was gone and both the nut and bolt were fine. Not even warm.
So basically, the longer the mission, the more hands-on and heavy equipment oriented the mission, the more likely you will need an arc welder.
On the other hand, the more likely you will need any given chunk of equipment also. So the bigger the mission, the more likely you will be bringing various manufacturing equipment. It may not be very far in the future that an arc welder might be produced in a 3-D printer. There are 3-D printers now that will print in a variety of materials, which can then be cured using heat or microwaves etc., to achieve a variety of densities and hardness. It shouldn't be that big a deal to print most of the parts of an arc welder, then add the wires from non-specific supplies of wire. Possibly a few metal parts might need to be fashioned using other tools. And there you are, one arc welder. Overall, depending on the weight and room requirements on the ship, it might be preferable to take the data to run a 3-D printer, and tanks of printer material, than to try to take every possible tool you might need.
Indeed, on certain types of mission, you might be able to obtain the raw materials to make "3-D printer ink" rather than transport it. Maybe you only transport stuff you are not confident you can obtain locally. On the moon, for example, there is not much hydrogen available. So maybe you must transport tanks of hydrogen, possibly as water. Then you count on getting nearly everything else you need once you get there.