I've got a few that aren't up here.
It's nice to plan ahead for lsd, get supplies. I recommend...
1.) Food and drink, if you start to feel sick at any time it's most likely because you haven't eaten in 6-10 hours. Just keep a few snacks and some water or your favorite drink in a backpack. I found that I like white chocolate covered pretzels, they're sweet and crunchy and easy to chew.
2.) A backpack or something similar is useful if you're leaving the safety of your own home.
3.) Glow-sticks are hardcore, just don't go waving them around in public if you don't want to attract attention. Unless it's a fireworks holiday or Halloween, they scream "I'm on drugs!"
4.) Writing/Drawing supplies, I recommend a drawing pad and a decent mechanical pencil. DON'T USE PENS if you get emotional on lsd, if you get really into a drawing (likely if you happen to draw something good) it can be very frustrating to mess up.
5.) Bubbles, as previously stated. The magic bubbles sound really fun, I'd never thought about those.
6.) Some herb, if you need to calm down it does the job and if it's good weed it might cheer you up more than you expect it to.
7.) Music, it's nice to experiment but make sure you have music that you know you're into. My taste so far ranges from Daft Punk to The Bloodhound Gang to The Beatles and a lot of things in between.
8.) A Partner, if you aren't sure of yourself on acid then you need someone who can comfort you and guide you out of a bad trip. Acid can literally drive people to madness and if you've had a history of depression or anger or have never confronted and beaten a serious problem it may be dangerous for you. If you're sure of your mental stability and you know that you will always be able to distinguish the real and the unreal then you're alright (at least that's my theory but who knows it's a crazy drug). A partner is good to have though, you won't always experience the same thing but the fact that YOU DO experience the same things sometimes is so mind-blowing.
9.) Some cash, you need cash in the real world. No, people aren't going to give you free shit because you want it. Seriously...
10.) Colored sunglasses. Viewing everything through a colored lens can be pretty cool.
Now, Activities. I won't be listing any of the great ideas that have already been posted, this post is already going to be longish and it's already been said anyhow.
1.) This is where my screen name comes from. I must warn you, BE CAREFUL IF YOU TRY THIS. You'll need some glow-sticks, some containers (cups work just fine), and a paintbrush.
First, you'll need to open the glow-sticks. BE CAREFUL, glowsticks contain hydrogen peroxide and produce phenol which is harmful to the skin and can cause irritation and may even cause nausea and vomiting. They're difficult to get into and can make a terrible mess so try this OUTSIDE unless you find a clean way to get them open. Don't break them, the fluid will go everywhere (it will look really cool but it will still be messy), cut them open with a sharp knife (the weight of a butcher knife or a machete works well). If you plan on doing this, PRACTICE opening one before you start tripping (OUTSIDE) so that you know what you're doing later.
Next, just pour the fluids into the containers (there are so many things you can do with this stuff but I'll leave the ideas up to you) pick up your paintbrush, and paint. That's right, it glows. It's cool.
2.) Just two follow ups on the glow-sticks. Try pouring the fluid in a bowl with or without water, mix colors, stir it around (use a stick or something, not your hands) it's fun but don't make a mess. When disposing of the stuff, flush it all down the toilet with the lights off, it doesn't last long but it still looks cool.
3.) Sex, it's already been stated but there are a lot of ways to spice it up when you're on acid. Glow-sticks, no don't use them on your partner (there's the slim chance they could break, unlikely but still) just have them around, use a strobe light or a black-light or colored lights or whatever you've got to add to the atmosphere. Turn on some music that fits the atmosphere you create. Lights aren't your only option either. If you're out in nature all you need is a blanket or a tent. The sun makes you feel so happy when you're tripping and it can lead to a surprisingly romantic setting depending on where you are. The night adds yet another atmosphere and there are so many places you can go day or night.
4.) Some people can handle being in public. Most of the time, I can straighten myself up enough to handle any situation whether it's giving a random pedestrian directions or telling a cop why I'm walking around in a nice high class residential area at midnight. Anyhow, if you can handle public places go somewhere fun. Arcades have a lot of lights and fun games. Theme parks have a lot to offer, I would LOVE to ride a roller coaster on acid but I haven't gotten the chance YET.
I wanted to shoot for 10 here, but this is already kinda long and a lot of my favorite activities are already listed. However, if I come up with something else I just have to share I'll be sure to post here.