Hey everyone, haven't seen much discussion on this topic yet so I'll chip in what I know and others can add/correct me. To start things off, your priority for spending coins should be as follows:

Items > Equipment > Skins

We'll go into some more detail on what items and equipment stats to focus on in this guide. I'm biased towards playing team/objective games in Wormis so keep that in mind while reading the guide.

There are really only two that are worth buying, and I'd only bother using either in guild wars but you do you. You can only have one item equipped at a time. To equip an item click on the space new to POW on your home screen, select the item, and press equip in the top right. I'm relatively sure that all items have a 90 second cooldown as well, so keep in mind that you have to use them strategically.

Major Petrifying Shoot (x3, 300g): Stuns an enemy for up to 3 seconds. Hug the snake's head tightly so they've got nowhere to turn after it and your golden

Lesser Immunity Shield (x4, 300g): Removes the harmful effects currently on your snake and grants immunity for 3 seconds. Save it for when you're stunned, and realize that in those 3 seconds you can not boost (like when you enter a game) so you'll need to navigate yourself carefully.

Double Malt Beer (x5, 300g): Kind of useful since the snake can lose some control, it makes their screen go blurry but the snake can still choose it's own direction. Still, the petrifying shot seems more useful. The only time that a Double Malt Beer could be better than the Petrifying Shoot is when the enemy snake continuously hides their head in their body and you need him to be exposed.

Strong Nets Launcher (x5, 200g): Slows an enemy. Pretty bad though and not that much of a hassle to the enemy.

Antiviral Shield (x4, 200g): Makes you immune to a virus (stuns, etc.) for 4 seconds. You have to use it before you get stunned though, so you either see a petrifying shoot coming at you and react quick or get lucky. Lesser Immunity Shield is worth paying more if getting out of the virus actually matters.

Ghostly Spyglass (x5, 100g): Extends how much of the map you see for 10 seconds. I never found it that useful but maybe others do.

Update: Some lower level items won't work on higher level snakes, which are most of the people that you're going to be trying to kill. Leveling up in the game isn't too bad so if you are in that position, just stockpile coins until you can get the good items

You've only got three gear spots that you can utilize. Gear is below items because the benefit of gear is still unclear as far as how much it really helps. Here are the different bonuses that stats give you afaik

Agility: Reduces turning radius
Eat Distance: Increases how far away you can be from food while still getting it
Eject Speed: Increases the speed that you can shoot food (...)
Fatigue Resistance: Allows you to sprint longer/lose less mass while sprinting
Initial Size: Increases how large you spawn on the map
Thinness: Makes your snake thinner than he would usually be
Virus Resistance: Increases your chance of resisting a virus

I would say that when you're choosing your gear you should think about what kind of a snake you want to be and build around that. If you value being small quick and attacking the big guy I would gear up on agility and mayyybe thinness (but really just agility). If you want to be a big snake who plays offensively I would go for Agility, Initial Size, and Eat Distance. If you want to be a big snake who's job it is to stay alive I would go for initial size, agility, and virus resistance. I can't speak about how effective virus resistance is but if you're trying to be the tank than it sounds like a good idea to get some stats in that.

To me, there are a few stats that are pointless. Thinness just makes you less able to throw around your mass, Fatigue Resistance only seems semi-useful in Catch the Egg or coin farming, and Eject speed just isn't needed ever. If anyone else has positives for them feel free to post.

For items repairs are usually pretty reasonable. Roughly 30g for an item you spend 2000g on in my experience. Every item has 1 durability that goes down one every time you enter a game (the first time or after death). You can sell your items back after buying them at a discounted price, and they get you a lot less money if they aren't at 100/100 durability.