Expeditious retreat, far step, hex, magic stone, misty step, shadow blade...
But since your slots are limited... Kind of iffy
I will break these down a little more if you don't mind 5ekyu.
Hex, shadow blade, and misty step don't use your bonus action after the initial use so its not really going to help your action economy because your not using your bonus action for anything else it means its easy to use them without waste. Not bad warlock options because you will have very little conflict casting them but with only 2 spell slots until level 11 your not going to get much bonus action use out of them and the are just not useful for the action economy usage the OP is asking for.
(Tome warlocks could get Shillelagh as a repeatable bonus action cantrip but it would only mean one bonus action every 10 rounds putting it in the same catigory)
Magic Stone is the only bonus acton cantrip that can be cast repetitively for any actual benefit but unless your feeding stones to a ally with a sling for 30/120 range due to lack of a ranged/magical alternative then its not very useful since it removes the effect from the previous stones when you cast, so you would have to stand next to your ally or do it yourself... as a warlock you likely have other more effective spells and this is a bit of a waste of a cantrip. ... well unless you name your warlock David then go for it. (Side note, It makes 3 stones so if your ally only has one attack like a rogue who might want it for sneak attack at range with free ammunition against enemies immune to non-magical damage you only have to cast it once every 3 turns possibly the best use for it however anyone with 2 attacks would need it cast every turn or be short an attack)
Expeditions retreat and Far step are the only options to get the action economy a warlock might want but they are both avoidance/pursuit abilities so they are not going to work all the time. If no one is running away, chasing you, or trying to corner you in melee they are using up your concentration when you could be casting something more fun and/or effective.
Due to warlocks lack of spell slots it is generally not worth the cost to use most bonus action spells unless they have a continual concentration effect, but then you have a second cost of it preventing another concentration spell you might need more. The other way to look at it is when you do use a bonus action spell with concentration it is basically never going to be a matter of having an available bonus action.