Battery & coInstall a same-size (or even larger) second battery for your extras, separated discharge-wise from the first battery through a relay - best of the voltage sensitive type. Here I would recommend BEP Marine.
This formula gives you an unexpected add-on benefit: You can jumpstart yourself, once your starter battery is approaching the end of its life cycle. All you need is a 1-lead jumpstart cable, so you can connect the 2 batteries' plus terminals.
When the time is there to exchange your alternator, look at the catalogue first to see if there is a stronger type available before buying the same type - like 120 A, instead of default 90 A. Not that it were indispensable, but it would be useful.
If you want to control the charge status of your second battery (advisable), you should get yourself a digital voltmeter. Here I would recommend Auto Meter.
If you have - regular or occasional - access to a mains socket, then it makes good sense to also install a charger, so that you can charge not only your second battery, but also the default battery, and in one go, should this become desirable. There are small and powerful chargers on the market, just see what you can find.
Recommendation: Make sure to establish all your 12 V connections based on the reliable ISO 4165 plug standard (see Google Images), not the cigarette lighter plug type. They are available as plugs, sockets and inline sockets. If nowhere else, you should be able to get them through both Bosch and Hella.
Now that you have a reliable infrastructure, you should connect your stereo system to the second battery, and independent of the ignition key. NB: Make sure you have a modern model, with the audio contacts on the front end. They also have an integrated isolation transformer, which means music listening from your notebook will not be affected through noise from a ground loop.
Mobile phone & coBuy a classic model, like the one from Peitel.
Then, get an external antenna. I use antennas from swedish maker Allgon, however they do not exist anymore. There are other makers, googling should get you there.
Mounting of phone and antenna can be done by any workshop featuring car stereos - even if they haven't done it before.
SAFETY TIP: If you can handle your car radio and a conversation with a passenger, then there should be nothing in the way for using a phone while driving. Simply make sure you use handsfree speakerphone mode, and trigger phone functions with 1 touch only. If you don't have a car with an automatic gearbox transmission, consider getting one - a car shifting automatically facilitates phoning considerably.
Laptop & coPlace your laptop on an elastic rubber mat, to keep it from gliding, and to absorb the vibrations. Lay it on its back to let some of the heat radiate away. To connect it to power, you can use a DC/AC inverter (12 V DC > 120/230 V AC), then use the laptop's mains plug. The Waeco brand can be recommended for quality inverters.
Regarding the screen, I recommend Xenarc, fx their 805YV model: Most of all it's light-weight, has a crystal-clear image, is electronically stable and looks good. Power it from your second battery.
Regarding mouse and keyboard, I would recommend wireless technology, fx Logitech M 187 and K 380.
Internet connection is established through a USB lead connecting laptop and the phone's black box. This is how it looks in practice:
0.00 Demonstrating wireless mouse and keyboard (due to my poor camera, the text I typed on the notepad did not become visible)
0.18 Launching Quovadis; can also be set to cover the entire screen, as shown here
0.57 Connecting to 3G internet (a 4G version is also available)
1.21 Browsing (Google, Youtube, newspaper)
In addition to what you just saw: According to the experience made, most people seem to think that, to access mobile internet (3G, 4G), you must have a 'smartphone'. This is not so. This european global mobile phone standard is designed such that you can connect a computer to any of its networks - provided they have not been manipulated with by the operator.
All you need is a mobile phone ('dumbphone', 'smartphone') to whose modem you connect your computer (desktop or laptop) - nowadays called 'tethering' -, and then you can access the internet from your PC as if it were at home or the office. The PC - phone connection can be made by either USB, BT, or wifi (hotspot). This is the principle I use in the car. And this is much more convenient than a tiny 'smartphone'. See how it looks like (the initially visible phone is the one which facilitates 4G-access, and to whose modem the laptop is BT-connected):
You can use your laptop also for other purposes, like audio and video entertainment. Another useful function is satnav. A good business specialising in this field is QuoVadis. It is sufficient to place its GPS antenna on your car's hat shelf.
This is the way the result looks like on the monitor, at a speed of about 100 km/h (on the motorway, which is the north-south road, starting at around 0.45 into the clip), for accuracy shown as a screencap:
It's the distance from about here
In this photo, you can see how the GPS software appears on the monitor, seen from the driver perspective (plus Winamp, for the music):
And the tune heard is an excerpt of a Steve Laury track called 59th Street.
Here another clip of the satnav situation, interrupted by a short reality interlude:
And one more in a city, by night:
SAFETY TIP: Start music and GPS before driving, and everything will run by itself. If you limit yourself during satnav operation to have the map moving with your rolling car (recommended, instead of active navigation), the only occasional manual intervention should be a change of the scale of your map, where necessary. You could stop for that if you don't feel safe to hit the button while driving.