Arch Linux is awesome, and if you are here, you probably already know what this is all about.
This is not a real guide, but a reference and recap.
Our objective is to create an Arch Linux USB that can boot anywhere, Macs and PCs, BIOS and UEFI, as lightweight as possible.
Notice: You should not just install the base package, I recommend the devel package too.
MBR (BIOS) only: http://lifehacker.com/5680453/build-a-killer-customized-arch-linux-installation-and-learn-all-about-linux-in-the-process
If you want to boot in BIOS with GPT, follow this guide when the above one comes to partitioning and installing boot loader:http://m157q.logdown.com/posts/2013/12/31/arch-linux-quick-installation-with-gpt-in-bios
If you want to also boot in UEFI, combine the above guide with this one: http://wood1978.techarea.org/~wood/wordpress/2013/08/08/uefi-systems-install-arch-linux-note
If you need dual-boot, create a new partition with linux filesystem, pacman "or-prober", use it and then run grub-mkconfig and then grub-install targeting respectively pc-i386 and efi as normal. Basically run or-prober before the installation of grub, same path and commands followed in the two articles, just that.
If you want to install a GUI, I suggest "Awesome wm": http://romans-it.blogspot.it/2013/06/arch-linux-with-awesome-wm.html
You'll be needing Slim (as seen in the previous guide). Slim and Awesome WM have a lot of customization, check the Arch Wiki posts about it.
If you need a Browser, the most lightweight and interesting at the same time is midori, however, I suggest Chromium, which has flash player integration and is quite faster.
If you want to download AUR packages without wasting time on building and stuff, check out yaourt (where you can download metasploit-git, the best option): https://archlinux.fr/yaourt-en
If you'd like to have interfaces shown as wlan0 and eth0 (pretty interesting in hacking automization), follow this:http://unix.stackexchange.com/questions/81834/how-can-i-change-the-default-ens33-network-device-to-old-eth0-on-fedora-19
Most common video drivers are
xf86-video-intel (for Macs too)
Try to install only the one you need or they might conflict (this happened to me).
Wireless card Drivers for Mac:
Pm-utils is a very interesting package that lets you enable suspension of the computer in RAM.
Finally if you want a very cool transparent terminal, my favorite choice is always "xfce4" with a lot of customization and interesting stuff, for example support (as xterm does) of commands at start with the -e option, very useful in an atomization enviroment.
And that's all for now, thanks for reading, and hope this helped.