*I usually tell my players to fill out their equipment lists before the game. It may take a huge amount of time, but as long as it is during "face time" it's fine with me.
* I enforce a rule that says that a healthy adult human can carry 55 pounds (~25kg for the rest of the world outside of the USA) on them for extended periods of time, provided that load is reasonably well distributed on the body (a backpack will suffice). I know a lot of RPGs have involved rules for encumbrance, based on body size or strength. I've found after talking with military people and those who do cross-country hikes or mountain climbing that things like body size and all that is irrelevant. A healthy human who is fit can carry 55 pounds without risking bodily stress injuries and so on.
* I "genericize" a lot of things in my games. For instance, yeah, an old audio modem can't transfer as much information as a modern satellite link, which in a game like Traveller might be covered by a bunch of rules and Tech Levels of equipment. I simply make up arbitrary calls on the fly "it'll take 1d6 rounds to transfer the information ... 4. So four rounds." In my Traveller games, for instance, I got rid of all the lower TL versions of items; it's a civilized region of space and characters are something to the exception to the rules and I assume they have ways of acquiring the highest TL versions of the equipment available (even if they're from some TL0 planet, they're the ones who are cozy with the Free Trader who lands on the world to trade or something).
That's for most games.
Recently, I've been experimenting with a new system I've thought of for a game for more "casual" players I've been running at the local game store.
I haven't worked out all the kinks yet, but it's based on an idea that I think we'd all agree with: Your characters have skills that the player of that character doesn't have. So it's kind of a jerk move for the GM to demand that, say, the doctor's player describe exactly how he's treating an infected broken leg. However, taking this one step further, if the character has the skills and not the player, shouldn't the character know what is needed for his or her job better than the player?
As a result, say that a character who is carrying 55 pounds worth of job-related gear has "full access" to gear for his or her skill related to it. Things like "mechanic", "combat rifleman", "mountain climbing", and "wilderness survival" the ones that come to mind at the moment.
These are pre-packaged bundles of items where I try and list what it'd typically contain within the 55 pound weight limit. I, with the help of knowledgeable players, determine what's in a bundle (I also determine the cost of the bundle). As I'm not an expert at these things, if there's something that isn't listed on the "package" list, but seems like it might be in the list, I may declare it's not in there (for instance, mountain climbers do use ladders as a kind of bridge to cross crevasses and so on - but that's not something they're typically going to bring) but usually I have the player make a roll vs. the skill in question with the difficulty determined by the unlikely or specialized nature of the item (as determined by me, though usually routine). If the player makes the roll, then the character is experienced enough to have predicted the need for the item and has it or has sufficient knowledge to quickly make an improvised work-around using the equipment he or she does have. Otherwise, no.
If the player has a split load (for instance, mountain climbing equipment and combat gear) the difficulties go up as they're sacrificing useful items to carry other gear. The assumption is 50/50 loads which increases the difficulty by a step. Because I don't want to deal with the granularity of 60/40 or 70/30 or whatever, I simply declare 50/50 is the only split load possible.
This system has worked out pretty nicely in that I no longer require players to keep track of individual shots in a magazine, nor do I need to make up mishaps when they fumble. There's three firearms fumble states: "temporary jam" (a dud round or something that requires a round to clear) and "major jam" (the unlikely serious roll that renders the weapon useless until it can be disassembled and inspected) is joined by a third result: Ammunition running low.
There's three ammo states: Normal, Running Low, Last Clip, and Out. The first ammunition "fumble" results in "low ammunition." The next fumble on ammunition means the weapon is on the last clip.
Normal is just that - they have sufficient reserves of ammunition that fire combat is conducted normally.
Running Low means the weapon suffers an additional difficulty bump for combat rolls as the user has the stress and distraction of trying to conserve ammunition on their mind.
Last Clip means the player is literally on their last few bullets. The next "miss" of a shot means they're out of ammunition.
A character with a similar weapon may split their ammunition with someone who is out of ammunition. If the giver is on normal ammunition, he or she drops to low (meanwhile the person who is out moves up to low). If the giver is on low ammunition, then they drop both drop to "last clip." People on their last clip may not share ammunition.
A player may only have one main weapon which follows these rules.
All secondary and specialized weapons start at low ammunition (but without the skill penalty), but the first ammunition fumble results in out instead of last clip.
I use a modified system for various consumable supplies in the 55-pound packs (especially medical supplies), but not food. However, consumables only have three states - so things like rope, climbing pitons, batteries, and antibiotics will always start normal, drop to "low", then run out. This means that a lot of "fumble" rolls can be explained easily - "you lose some of your rope and while you have enough to go on, it's on your mind now." Obviously, it's not such a big deal with rope because if every character is carrying rope, everyone can use just one rope to climb up.
Food is always measured in number of meals (with field combat packs containing 9 meals worth of food). A further 12 meals can be carried as a "split load" (as per rules above).