I know some groups take great pleasure in the meticulous counting of coin, in haggling in the marketplace or with the innkeep... while others almost completely ignore the accounting side of things. I'd be interested in hearing the ideas others have when it comes to dealing with such things.
In our group in the past we've tried a few different things, but we finally came up with this: generic supplies and spell components, anything under 100 gp really is assumed to be available and coin is not tracked closely tracked except in the hundreds or thousands. It lets the group search bodies for valuable info but not have to loot every dead goblin of every bent copper and speeds up adventuring for the most part.
For rarer and more unusual items like spell components, potions or minor magical items - I don't allow major magic items to be casually purchased - I tend to make them have to go through the effort of establishing contacts in order to buy things like potions or special items, perhaps go in the occaisional quest for rare ingrediants to stay in good stead with their suppliers... for extended forays, like through the dessert or in the Underdark if the characters are unable to resupply or make no effort to do so, I have a short list of things that I randomly roll on for them to 'run out of' at periodic intervals, each item carrying with it a penalty that lasts until they manage to make arrangements to resupply.
1 - Food. Food needs to be rationed. While its being rationed, characters must make a Fortitude save each day or become Fatigued. If this result is rolled a second time, food runs out completely and characters must make a Fortitude save each day or become Exhausted until they get food.
2 - Water. As above with Food.
3 - Ammunition runs out. Standard arrows (or some other sort of ammunition) has run out and ranged attacks can't be made with those particular ranged weapons until they are replaced).
4 - Spell components run out. Generic spell components are running out. There is a 50% chance that a spells requiring generic components can not be cast until they are resupplied.
5 - Nothing runs out.
6 - Nothing runs out.
I don't try to make life hard on my players, don't want them to have to meticulously track every bit of minutia, but I still want there to be some realism in the simple survival aspect of the game. Obviously if steps are taken to alleviate these concerns (Decanter of Endless Water, Rings of Sustenance, the feat Eschew Materials or ranged weapons that can't run out of ammunition), then that particular penalty is negated.
Like most things, I take a practical approach to these things. Unless there is a plot reason to worry about the quantity of supplies, then we just have a standard 5gp a week cost to replenish supplies and pretty much ignore them.
However, if there is a plot reason (the party has to take an extended period of time to explore a remote cavern, cross a desert, make a trip in a boat, etc...) then we track things pretty meticulously. Not everything, but the important things.
What this usually means though is that there is a spell tax on the party to replenish supplies magically.
I don't think you need to keep track of how much breakfast, lunch or dinner usually cost. The price can usually be bundled with the cost of the Inn.
If you are out and about town and splurge on a meal, even if its a few silver, I think it's worth the time figure the cost of things because it's non-routine, such as a character takes a local out on a date or something.
I agree, if you are getting supplies for a long out-of-town dungeon dive, you should keep track of what you spend on gear, even if it is just mundane things like rations or pots and pans.
I don't think it's too hard to keep track of coppers and silver, but that's just me. You usually just spend gold pieces, so the rare time you spend silver or copper pieces isn't a big deal to tally for me.
What really can bog down a game is factoring the weight of coins or how is a character carrying all those coins. That can really take away from the actual campaign. At some point, players should convert to gold to gems, but figuring out how much 20 gp 4 sp and 8 cp weighs just doesn't seem to be a good use of time to me.