Crates

The crates are the box-like objects that appear in all C&C games and grant bonuses (or 'surprises') to the player that collects them by sending a unit into the same cell as it.

The crate functionality is described by two sections - CrateRules and Powerups. To each it's turn:

CrateRules

This section covers generic stuff, like how often to spawn crates, how many of them to spawn, etc. It has lots of comments, so every tag should be self-explanatory.

[CrateRules]
CrateMaximum=255 ; crates can never exceed this quantity
CrateMinimum=1 ; crates are normally one per human player but never below this number
CrateRadius=3.0 ; radius (cells) for area effect crate powerup bonuses
CrateRegen=3 ; average minutes between random powerup crate regeneration
SilverCrate=HealBase ; solo play silver crate bonus
SoloCrateMoney=5000 ; money to give for money crate in solo play missions
UnitCrateType=none ; specifies specific unit type for unit type crate ['none' means pick randomly]1
WoodCrate=Money ; solo play wood crate bonus
WaterCrate=Money; solo play water crate bonus
HealCrateSound=HealCrate; heal crate sound effect
WoodCrateImg=CRATE ; wood crate OverlayType image to use
CrateImg=CRATE ; normal crate OverlayType image to use
WaterCrateImg=WCRATE; Water crate image
FreeMCV=yes ; Give free MCV from crate if no buildings but still has money [multiplay only]?</pre>

Powerups

What you get out of a crate is dictated by the [Powerups] section.

[Powerups]
Armor=10,ARMOR,yes,1.5 ;Unit's Strength= is multiplied by the param#4
Firepower=10,FIREPOWR,yes,2.0 ;Unit Weapons' Damage= is multiplied by the param#4
HealBase=10,HEALALL,yes ;All the player's stuff goes to 100% health
Money=20,MONEY,yes,2000 ;Random amount of cash(max amount = param#4)
Reveal=10,REVEAL,yes ;All map is revealed
Speed=10,SPEED,yes,1.2 ;Unit's Speed= is multiplied by the param#4
Veteran=20,VETERAN,yes,1 ;Unit is promoted(through as many levels as param#4 says)
Unit=20,<none>,no ;Random unit is given1
Invulnerability=0,ARMOR,yes,1.0 ;Nothing happens2
IonStorm=0,<none>,yes ;Nothing happens2
Gas=0,<none>,yes,100 ;Tiberium Gas effect3
Tiberium=0,<none>,no ;A random patch of Ore is created at the cell
Pod=0,<none>,no ;Nothing happens2
Cloak=0,CLOAK,yes ;Unit is cloaked (like the Stealth Tank/Submarine)
Darkness=0,SHROUDX,yes ;Map is reshrouded
Explosion=0,<none>,yes,500 ;An explosion deals param#4 of damage, warhead unknown
ICBM=0,CHEMISLE,yes ;A ready one-shot Nuke is given if you don't have it
Napalm=0,<none>,no,600 ;An fire explosion deals param#4 of damage, Warhead=Fire
Squad=0,<none>,no ;Nothing happens2. In RA2 and YR, it instead functions as a second Money.

The first parameter dictates the chance of getting this kind of crate. It does not mean %, it means 'param#1 shares out of all possible shares'.
The second one says what animation to play.
Third one says if this crate can be found on water.
The fourth one varies by crate.

Problems

Certain naval units contain CrateGoodie=yes, or don't include the tag at all. The game does not differentiate between naval and ground vehicles, and a unit crate might give you a naval unit on a no-water map, resulting in an Internal Error. If the map does contain water, though, the naval unit will be spawned in the water without the error. So best to set CrateGoodie on all naval units to no (note, originally the Destroyer lacks this tag, so fix it too).

¹ ↑ If this is set to 'none', a random unit is picked randomly from an array of units with CrateGoodie set to yes.

² ↑ The animation is played anyway, and since you can attach a Damage to an animation as well as MakeInfantry, you can get all kinds of effects from that...

³ ↑ Later Update: A poisonous green gas explosion deals param#4 of damage using the Gas warhead, ((The animations GasCloud1 and GasCloudD1 are broken by GEF, they must be fixed in order to work. also CLOUD1 and CLOUD1D have wrong pallete)