Whether a player or game master, keeping up with the vast amount of info communicated in the course of a tabletop campaign can be daunting. As a player I'm a compulsive note taker; if I don't write it down, I forget it. And you better believe if it's something like how large a reward the quest giver promised the party I'm noting that down. For a long time, OneNote has been my go-to for this. Syncing between devices, multiple notebooks, sections, subsections, etc. It's got most of what you need to take notes on anything, but is well suited a long Dungeons and Dragons campaign.
However, as a dungeon master, I struggle to keep all the info I need in front of me. At a given moment I might need all of the following at the same time:
It's a lot, and usually those things are all in separate places; maybe I have the party summary on a note card and the monster stat blocks printed out. Then the initiative order is in a notebook. The DM map and area descriptions are in the source book, but on different pages. Rules I can reference, but they're in a separate book. Where did I put those monster stat blocks again?
In combat I feel like I'm constantly losing my place. But no more! I've manage to condense all those disparate sources into two sources of truth: Kanka.io (for DM maps & area descriptions) and D&D Beyond (for everything else). This is not yet a battle tested solution, but I wanted to document it, because I'm really happy with it so far. It takes some setup and would certainly work best with a pre-published adventure, but I think it's worth it.
"My Encounters" is probably my favorite new feature on D&D Beyond that (at time of writing) requires a subscription to use. I've had great luck with the Master tier subscription, since it allows me to share my purchased content with all the players in my campaign. Add your monsters, select the campaign the encounter is for. After asking players to roll initiative, I can quickly enter their results and auto roll for the monsters. If at any point I need to adjust HP here I can (without doing math!), and clicking on the monster brings up its stat block.
Here's where my plan falls apart. Player character summaries and dice rolling are both in active development for this page and not available yet. Bummer. So for now I keep a set of tabs open for each person's character sheet and use the dice there to roll attacks against them. However, I expect these features soon since they are both included in recent D&D Beyond Dev Updates.
That's what D&D Beyond is for. I use the search here liberally.
And here it is, the thing that's saving me tons of time correlating an area's number to its description: Kanka's interactive map tool.
On Kanka, you can upload a map for each location. That map (like everything else on Kanka) can be set to private to let only Admins (read: DMs) see it. For each area, I create Notes for each map location, copied directly from D&D Beyond. Enabling edit mode on the map allows you to create and place interactive pins on the map, which show a short description from the note, and link to it. No more flipping back and forth between pages; just click and you're there.
Beyond this use, Kanka is basically a fancy wiki that your players can contribute to as well; I'm encouraging mine to keep track of different NPCs there and am keeping all handouts there. I've created entries for all the various characters they might encounter (along with some they might not!) that I will reveal when needed. Each character can have a picture (both for my and my players' sakes) as well as a hidden personality description so I know how to roleplay each one. Plus, it's free version seems to have more than enough functionality for me and my group.