Micro jQuery Plugin
If you want your own chainable clickToggle jQuery Method you can do it like:
jQuery.fn.clickToggle = function(a, b) {
  return this.on("click", function(ev) { [b, a][this.$_io ^= 1].call(this, ev) })
};
// TEST:
$('button').clickToggle(function(ev) {
  $(this).text("B"); 
}, function(ev) {
  $(this).text("A");
});
<button>A</button>
<button>A</button>
<button>A</button>
<script src="//code.jquery.com/jquery-3.3.1.min.js"></script>
 
 
Simple Functions Toggler
LIVE DEMO
function a(){ console.log('a'); }
function b(){ console.log('b'); }
$("selector").click(function() { 
  return (this.tog = !this.tog) ? a() : b();
});
If you want it even shorter (why would one, right?!) you can use the Bitwise XOR *Docs operator like:
DEMO
  return (this.tog^=1) ? a() : b();
That's all.
The trick is to set to the this Object a boolean property tog,  and toggle it using negation (tog = !tog)
and put the needed function calls
 in a Conditional Operator ?:
In OP's example (even with multiple elements) could look like:
function a(el){ $(el).animate({width: 260}, 1500); }
function b(el){ $(el).animate({width: 30}, 1500);  }
$("selector").click(function() {
  var el = this;
  return (el.t = !el.t) ? a(el) : b(el);
}); 
ALSO: You can also store-toggle like:
DEMO:
$("selector").click(function() {
  $(this).animate({width: (this.tog ^= 1) ? 260 : 30 });
}); 
but it was not the OP's exact request for he's looking for a way to have two separate operations / functions 
Note: this will not store the current Toggle state but just inverse our functions positions in Array (It has it's uses...)
You simply store your a,b functions inside an array, onclick you simply reverse the array order and execute the array[1] function:
LIVE DEMO
function a(){ console.log("a"); }
function b(){ console.log("b"); }
var ab = [a,b];
$("selector").click(function(){
  ab.reverse()[1](); // Reverse and Execute! // >> "a","b","a","b"...
});
SOME MASHUP!
jQuery DEMO
JavaScript DEMO
Create a nice function toggleAB() that will contain your two functions, put them in Array, and at the end of the array you simply execute the function [0 // 1] respectively depending on the tog property that's passed to the function from the this  reference:
function toggleAB(){
  var el = this; // `this` is the "button" Element Obj reference`
  return [
    function() { console.log("b"); },
    function() { console.log("a"); }
  ][el.tog^=1]();
}
$("selector").click( toggleAB );