Lets talk about immediate modifications that you tend to do with any car once you add it to the fleet. I have a few things that pretty much every car needs in my list but I would love to hear what everyone else does too. Personalization goes a long way towards making new ownership more emotionally enjoyable for me, and I bet some of you are the same way.
Stuff I do quickly to almost all cars:
Spot Mirrors - usually smallish (2") round adjustable mirrors get stuck on each side. These are great for minimizing new blind spots and in tight city confines they are infinitely useful. Almost all cars could have better mirrors but for a few bucks and five minutes this is an easy upgrade.
Window Shades / Vent Visors - Whatever you call 'em, I like 'em. Being able to quickly install these tinted plastic covers over the windows makes the cheap buy in a no brainer. I like to be able to leave the windows cracked an inch sometimes, even in rain or snow. Being able to open them halfway in the rain without getting soaked is very nice if you like a little air in you face or smoke while you drive. Some cars seem to be designed to dump leftover rainwater directly on your forearm upon the first turn you make in the morning, and that sucks.
Tint - I usually go about 20% on every car, once you get used to it going without it very strange. Luckily, there are no strict laws where I live but be sure to check your area first; I have had issues in the past. I really like the additional privacy and it definitely keeps things cooler in the summer. Also, it can help with the headlights beaming into your brain on the highway when in a lowered vehicle or in front of a gigantic road whale suv with misaligned aftermarket eyeball lasers... Limo dark, colored or even weird reflective stuff is not my style but I suppose it can work in some situations.
Floor mats - If I can get something perfectly fitted and high quality I am pretty happy to pay the premium over almost anything else. Weather tech makes some good ones that contain everything from mud, snow/ice/slush to spilled coffee or anything else plus they stay in place really well. I really do not care about the condition of my carpets that much but I love to not worry about it, even the back seats get them too. They get stained, stinky and full of crap but a quick shot with the power washer and they are good to go back in for more abuse.
Filters - I have moved away from fancy cold (hot?) air intakes on modern cars simply because the factory engineered systems are usually pretty darn good these days. I still usually drop in a K&N factory replacement right away pretty much every time. I like that they are easily serviceable so that I can just clean them up whenever I feel like while working on something else on the car; no need to make an extra run to the store or hunt down a decent quality paper filter. Some paper stuff is not even really that cheap anymore and the serviceable lifetime filter wins in the end. Also, if I gain 1-2 hp (tops) or make then I feel like that is money well spent. Air cabin filters also get changed immediately too if so equipped. The interior detail almost goes without saying but I never skip the last step of a new oem quality cabin filter for a little peace of mind. SWMBO loves this thoughtfulness as much as she hates germs!
Power! - No, not that kind! Electricity. I typically have enough 12v adapters, cigarette usb plugs, etc. or small inverters sitting around somewhere to make the car fully able to charge up any combination of things I need it too. Phones, laptops, tablets, mp3... whatever it is I like being able to keep it going strong.
Steering wheel - This is the part I touch the most (besides seats, which can be a lot more work). I hate crappy, falling apart, sticky or flaky unloved wheels in my hands or even touching my leather driving gloves. Aftermarket parts store covers are usually even worse. My go to solution is usually a leather wrap of decent quality with a full diameter stitch up tightly done the best I can. Nothing beats leather for me either bare handed or gloved. Stitching them up can take a while and maybe even some stop and restart efforts but is usually pretty cheap and worth it every time you hop in.
I could probably think of some more but I cannot continue to type a novel right now. I want to hear what others like to do when they get something new so that they can enjoy it more and make it "their own". There is nothing like buying a car for a grand and then putting more than that into it immediately, right?