Now, as many know, SteamWorld Dig has only a limited amount of money, since the Caves are rather thin. There are only five penalties for dying: You lose your stuff like in Minecraft, You're returned to the surface (can be a good thing), you're restored to your default meters (2 Bars health, Steamless, 2 Bars Torch), your Death Count is saved (and gets you a lower badge for Deaths), and the most important for this guide: YOU LOSE HALF YOUR MONEY ON-HAND! When you only have a few dollars on hand and a couple ores, nbd nbd. But when you have a bag full of Diamonds, a few grand you were saving for an upgrade, and you're extremely close to a randomly spawned Teleporter, it's extremely irksome. So, how do we make the inevitable mistake easier?

First, don't save too much money.
Now, I know what you're thinking: "But if you don't save a few hauls worth, you can't buy anything!"
Yes, it's important to save SOME money. However, try to prevent having a surplus. If you're going for a $1,500 upgrade, have $1,300 on hand, and at least 200 in ores, stop digging downwards, or AT LEAST avoid that Moonshiner. Everybody dies at least a few times in their hundreds of playthroughs. If you have enough for a target upgrade from combined cash on hand and Pack value, be extra careful and return to surface soon.

Some people (including myself) don't like to return to surface until their pack is full. But if your meters are low (glowing, mainly Health), then ignore this in favor of the previous rule.

WARNING: The following segment is an enormous wall of text, which I have noticed while proofreading. Important points are bolded, and the rest can be skimmed through though it is recommended that you read it fully to gather as much as possible. Since it is rather wordy, I probably made a few grammatical errors, and will fix them if pointed out or if I notice them myself. Thank you.

First and most important is when to by which upgrades. If you work hard enough and be careful enough, you can get all upgrades in the end. But, many upgrades are more important than others, and circumstances call for certain upgrades. You should mainly follow the priority list later in the guide, but it's ok to deviate from that if circumstances call. If it takes half a unit of Steam to mine a single Hard Dirt block with the Drill, upgrade Drill before your next armor. If there are two upgrades and one has twice as many orbs that you have.

Here's a scenario: You have 2,000 gold, 5 orbs and you just came back from a Bonus Cave. One item costs 1,500g and 5 Orbs and is a tad less useful, the other 1,750g and 10 orbs but is phenomenally useful. Go for the cheaper one, not just because it's cheaper but because it's closer in your price range for orbs, especially considering you JUST got back from a cave that gave you a few (probably all five of them).

It may seem nonsensical, but you should use excess Gold before going on a wild goose chase for Orbs. If you just went back to town, it probably means your bag was full or you're in critical condition. This, however, is usually overruled if you know where an Orb ore is (within a reasonable distance from an entrance).
Large wall of text is over. Please make sure to read everything thouroughly from now on.

ORE MANAGEMENT
This is FAR more basic than anything else here. A quick summary is "don't throw ores away, and stop mining when your pack is full (unless you have no other choice)." But there is a crcumstance. If you're through Old World, then go ahead and throw away anything from Archea if you need more space for something more vauable from at least half through Old World. Trashium, on the other hand, is just that. Trash. Don't bother after early game.

This section is rather complicated. Here's an explanation:
Each number represents a "Tier Point". Tier Points describe how important an upgrade is compared to others. If an item has x more Tier Points than another item, then you should prioritize it more by x Upgrade Tiers. 0 Points means to never buy that upgrade unless completely necessary An Upgrade Tier is determined by how many of that upgrade has been purchased. An Unlockable Upgrade's first tier is equivalent to the level that it's unlocked at.

Finally, there are certain circumstances that can add tier points:
+1 to Digging Upgrades for every 5 terrain levels (5 hits to hard dirt=+1 in Digging)
+9,999 to Refill Health if health is very low
+3 to Steam Usage upgrades if 1 bar of Steam is used in less than 10 seconds of standard Drilling in Hard Dirt
+2 to Armor Upgrade permanantly when a new area is reached
+1 to Usable Items for each of that item below the maximum (nix Torches and Teleporters)
+9,999,999,999,999 x Infinity to Torches if you never want to use that profile again
+1 Priority to every category for every 25% cheaper it is (except Usable Items, Torches, Teleporters, and Refill Health. Note: Orbs translate to 500 Gold when calculating this.)
+5 Priority to Combat and Meter Upgrades when preparing for the Final Boss (spoiler-free for people who spent less than six hours total learning or playing this game)

So, on to the list.

2-Pickaxe (digging)
9,999,999-Sharper Pick (digging)
2-Faster Pick (digging)
1-Lantern (digging, meter)
4-Drill (digging)
3-Bag (bag)
3-Steam Punch (digging, combat)
2-Hydraulic Fluid (combat)
4-Armor (combat, meter)
4-Tank (combat, meter, digging, steam usage)
3-Water Seal (steam usage)
0-That thing that makes Steam Jumps cheaper that no one uses (steam usage)
1-Ladders (usable items)
0-Dynamite (usable items)
Negative Infinity-Torches (torches)
0.5-Teleporter (teleporter-only purchase if you want a really quick game as a pro or during any game as a noobier person. Seriously, there are 2-3 per area naturally spawned, even maybe 4 in Vectron!)
0-Refill Health

Hey, thanks for reading my guide! Leave a like if you enjoyed it, and favorite it if you want more! I am currently open for requests that aren't achievement-related.
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Also, remember to check out my other guides on SteamWorld Dig!
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If you noticed any mistakes, or want to add anything, tell me in the comments section!
FAREWELL!