redux saga selectors, how do I access state from a saga?

You will have to use selectors for that. I’ll give a simple example.
Create a file selectors.js and add the fields you want to select from your store, as shown below.

export const username = (state) => state.user.name;

Then in your saga, import the selectors as,

import * as selectors from './selectors';

and when you require username in your saga, you can simply do,

import {select} from 'redux-saga/effects';
...
...
function *sampleSaga(params) {
   const username = yield select(selectors.username);
}

the constant username in sampleSaga will now hold the username value from state.