Caffeine

Item	Time	Caffeine	Time/Caffeine	Autosell	Notes
Brad energy drink	20	4	5	5	April Fool's 2008 item
- all coffee shop items -	30	3	10	varies	Coffee Snob Merit Badge
Coffee mochi ball	30	3	10	32
Smart juice	30	3	10	15	+10xp
caffeine pill	25	2	12.5	30
Vial of powdered mojo	50	4	12.5	30
Can of Gingerelle	15	1	15	1	Black Market item
Can of Gingerette	15	1	15	1	Black Market item
Gingerette Black	30	2	15	30
Bag of PG Tips	45	3	15	20
Pep-up pill	60	4	15	30
Guatemalan pepperjuice	35	2	17.5	120	Gives effect: The Sweats 35 minutes
Dose of X-presso	35	2	17.5	30
Mister Tea	105	6	17.5	50	Black Market item
Blue Oxford drink	36	2	18	80
fortified coffee	90	5	18	32
Oil can coffee	+?-62-74-?	4	NA	25
Rainbow's Ark pill	55	3	18.333	110
White pill	180	8	22.5	10	Gives effects: Euphoria 60 minutes Utter Wretchedness 240 minutes
Exigen-C cocktail	95	4	23.75	150
Bray energy drink	120	5	24	50	Flight Simulator reward
Scalpel energy drink	120	5	24	50	Virtual Sports reward

Analysis

Caffeine toleration is your character's maximum level of caffeine per day. Every item has a set caffeine level, and every person has a set caffeine toleration of 12 (unless content comes out that alters your caffeine toleration). As such, knowing the caffeine level of an item can help you see if you're wasting chips/caffeine in your day. While some items may appear to be less effective, it may end up that due to their caffeine level, they're more useful than a higher time yielding item. The basic calculation for efficiency is to take 12, the caffeine toleration, divide it by the caffeine level, round down, and multiply it by the time given. This, of course, does not take into account difficulty to obtain items or bad side effects. Here's a rough chart, in order from least to most effective, effectiveness being higher for items that you need to use less of for the same amount of time (for convenience, denote coffee shop items as being every item in the coffee shop except the herbal tea):

coffee shop items: 2 hours
caffeine pill: 2.5 hours
Vial of powdered mojo: 2.5 hours
Can of Gingerelle: 3 hours
Bag of PG Tips: 3 hours
Pep-up pill: 3 hours
fortified coffee: 3 hours*
White pill: 3 hours*
Guatemalan pepperjuice: 3.5 hours
Dose of X-presso: 3.5 hours
Mister Tea: 3.5 hours
Blue Oxford drink: 3.6 hours
Rainbow's Ark pill: 3.667 hours
Bray energy drink: 4 hours*
Scalpel energy drink: 4 hours*
Exigen-C cocktail: 4.75 hours

Notes

*Brays and Scalpels leave room for 2 caffeine left, which means 2 gingers would bring it to 4.5 hours, or 1 pepperjuice would bring it to 4 hours and 35 minutes. Fortified coffee leaves room for 2 caffeine as well, so it could be brought up to 3.5 hours a day, or 3 hours and 35 minutes, with the same items. White pills leave room for 4 more caffeine, which brings their total to 4 hours with gingers, or 4 hours and 10 minutes with pepperjuice.

A Coffee mochi ball yields the same results as coffee shop items. The Can of Gingerette yields the same results as Can of Gingerelle. The Scalpel energy drink yields the same results as the Bray energy drink. The Dose of X-presso has the same yield as the Guatemalan pepperjuice but without the bad side effects. The white pill has a good side-effect (Euphoria) and then a very bad side-effect following it (Utter Wretchedness), so it's best to think carefully before using.