The main thing is to be organised. Less is more and what you have you need to be able to access easily.
When I first started I had a small, standard backpack and I found it quite difficult to access my gear and get the lure I wanted whilst wading.
I soon moved to a "sling bag" (there are a few out there, I went with the rapala version). This allowed me to easily slide/swing the bag from my back, round in front of me without having to take it off. Other options would be bum-bags (black magics come to mind), small satchel bags (Diawa), the Alvey wading bags, and even fly vests @Meppstas gave me that one when I was first looking around and I later found it is also what Bushy uses when wading.
I then upgraded to a tub (blatantly stole this from @Underpants) - which makes things easier again. It also allows me to cheat by having 3 different rods, all rigged with different lures which means Im changing less lures on the water.
Regarding changing of lures and frequency. When I first started, I changed as often as possible as I wanted to speed up my learning - which lures/patterns/retrieves worked best in which scenarios. The biggest problem I ran into wasn't actually changing the lure, it was running out of leader. Changing a lure on the water is easy. Tying on a new leader whilst on the water is a pain in the a$$, especially when its windy!! Once I moved to a tub with multiple rods, I had 3 times as much leader to play with - cheating really .
If I had my time again, or I was advising someone just starting out. My advice would be this.
1. Less is more. No need to take the kitchen sink. A small tackle tray that holds a handful of lures is more than enough. 2-3 stickbaits and 2-3 poppers will provide enough variance but still allow you to focus of nailing their retrieves.
2. Get a small bum-bag (just because they are cheaper) that can hold the tackle tray, scissors, a spool of leader, small pliers, suncreen and your car keys. Bum-bag goes over one shoulder and under the arm of the other. Creates a "sling" action and you have everything at the ready.
3. Pick a braid-leader knot and direct leader to tow point knot and practice them at home. I dont mean sitting down with the rod over there and your leader spool beside you. I mean practice as you would on the water. Rod tucked under one arm, standing, gear bag on. Otherwise its a long walk back to the bank to deal with it each and everytime.
4. Just keep casting. Persist, persist, persist. Like anything, once you crack the code its sooooo much fun.