This is a list of what rules are in use for my GURPS Star Wars game...at least, the Tenloss Syndicate one. Depending on future genre and tone of other games in the setting, these may change. Not all of these are optional rules, some are important rules that I felt needed to have their implications pointed out and where to find the rules for whatever.

We'll begin with:

GURPS Basic Set: Campaigns

p.B420, Bleeding: This optional rule is in use. Hard to Kill and Hard to Subdue, do not apply to the Health roll, Fit or Very Fit (as well as any special modifiers for coagulants or alien racial perks, etc.) do apply.

p.B407 Special Ranged Combat Rules, Malfunctions: This rule is in effect. Note that for beam weapons,  Stoppages are treated as Mechanical/Electrical problems. For this purpose this means that (like revolvers) if a blaster, sonic weapon, etc. malfunctions, it malfunctions HARD--you're not likely to get it working again outside of a dedicated repair session. Two is one, one is none, as they say.

p.B420: Important note! If you take enough damage in the face, skull, or eyes, or vitals for enough damage to cause a shock penalty, you must make a knockdown roll. Knockdown rolls are at -5 for the face, -10 for the skull or eyes--but this penalty only applies to major wounds. Lesser wounds are normal knockdown rolls.

p.B366: Wait maneuvers can only be transformed into All-Out Attack, Attack, Feint, and Ready maneuvers.

p.B364: The Aim maneuver allows a step. You cannot step with a two-handed, braced weapon (but see rifle slings p.HT164).

p.B387, Facing Changes and Movement Costs: I found this enlightening as to movement costs.

GURPS Fairbairn-Sykes Close Combat System

p.14-15FSCCS, Testicle Grab: This technique is available in this game. Maybe all my games. That one paragraph made the .pdf worth $8.

GURPS High Tech

P.HT66, Concealing Armor: Ignore these rules until further notice. They're really, really out of whack.

P.HT79, Firearm Quality: These rules work the same way for blasters, sonic stunners, tanglers, etc. as for familiar mechanical, gunpowder-based firearms.

p.HT81-82, Drawing Your Weapon and the modifiers there for when drawing weapons from various positions.

p.HT93, Pistol Whipping: This can be done with a weapon of up to Bulk -3. Additional Bulk penalties from extended magazines, scopes, silencers, etc. don't count for this purpose. Otherwise, use Staff skill (p.HT198) to hit with the butt of a rifle-sized weapon.

p.HT198, Sheaths: These rules are in use.

p.HT249-252, Appendix: Gunmen, everything except what's labeled cinematic. 

GURPS Martial Arts

These optional rules are in use: p.MA68, Targeted Attacks; p.MA80, Combinations; p.MA100 and p.MA 109, the uses of Evaluate under Countering Feint and Deceptive Attacks and Evaluate and Non-Combat Skills; p.MA100, the bit under Feints about resisting with your best skill, not just the one you're using, and Beats (same page) for unsubtle attempts at removing defenses.

See p.103 Fast-Draw from Odd Positions and p.MA104 Quick-Readying Nearby Weapons for grabbing weapons during surprise attacks.

p.MA111 Reversed Grip allows for a tad more impaling damage and the use of unarmed parries.

For alien monsters, animals, and toothy sentients p.MA115, Teeth will be a useful reference.

p.MA118 Shoving People Around; p.MA119, Pain in Close Combat;and p.MA118, Grab and Smash! allow for hostage-takers (literally) strong-arming someone.

p.MA137, both New Hit Locations and Notes for Existing Hit Locations are in use.

p.MA144-146, Choosing a Style, and p.MA184 The Purpose of Military Hand-to-Hand are helpful for designing characters.

The rules for Hidden Weapons, p.MA218; are useful for sneaking weapons past security...

GURPS Spaceships

p.SS31-33: The only design switches used in this game are:

-All force screens are Adjustable at no extra cost, unless the screen is Partial.

-Force screens may be bought with the Energy or Kinetic limitations.

p.SS63, under Action Aboard, note the Internal Movement table and how long it takes to get to action stations per size of ship and turn length. Our standard turn length is 1-minute. 

GURPS Spaceships 2

Some of the material here will come into play occasionally, for example, the details in Port of Registry, Docking and Service Fees, and the rules for Cheap and Used Ships.  

GURPS Spaceships 3

Almost none of the rules here are useful (the four or five pages of fluff at the beginning, is)...the whole hex-grid system, well...it might be fun as a wargame or something, it's not, IMO, useful for space combat in an RPG. Or at least one I'd like to run or play in.

GURPS Spaceships 4

Closing Strategy: Reversal (SS4p.30), Landing On A Spacecraft, Space Piloting Techniques (SS4p.31), Fuel and Ammunition Transfers (SS4p.32), Cockpit Multitasking (SS4p.32), Crash Landings in Hangar Bays (SS4p.34) and Relative Target Size (SS4p.35) are all in effect.

Relative Target Size will only be applicable to most weapons on, for example Star Destroyers and Mon Cal Cruisers. Point Defense batteries will be unaffected...but whether or not an SM+17 Imperial-Class Star Destroyer is particularly worried about missiles that aren't nukes or antimatter warheads is another story...of course, large ships are designed as their own mini-fleet, with frigates, corvettes, etc. to tackle the "glob flies".

OTOH, the new Bomb rules allow for a LOT more bombs to be carried than missiles...

Environmental Effects (SS4p.35-36): Definitely seeing some use in the future. Rules for fighting in low orbit, cinematic nebulas, ion storms and gas clouds, and Unpredictable Debris Fields (comet tails, gas giant rings, tight clusters of space stations and satellites, and recent battle wreckage...).

GURPS Spaceships 5: SS5, p. 27 Small sensors Drones and Probes.

GURPS Spaceships 6: SS6, p.6, Refitting and Repairs. Repairing a single system counts as a repair. Multiple systems count as a refit. Time for a refit is 1 day per dHP of the ship. This can be decreased by paying more (see SS6p.4). Triple the price reduces time to 2/3s, quadruple the price halves the time required. This may require negotiation with business owners, union officials, etc.

GURPS Spaceships 7: We are now using the Electromagnetic Disruptors rules (SS7p.30) for ion cannons.

Also, the rules for Larger and Smaller Systems (p.4-5), Holoprojector (p.10), high- and ultra-tech Jet Engine (p.10), Maneuver Enhancement (p.11), are in use, as are the Design Features Hidden Weapons Batteries (p.20) and Lacks Automation (p.20).