The original maneuver that evolved into the bench press was not done with any more equipment than a barbell. While floor presses today are usually received from a rack which is low to the ground, the press of olde was mounted by an initial hip thrust (Figure 1) to put it into a favorable position for either bracing or pressing with the arms.[1] It was a much more dynamic movement than the bench press of today, as in many settings it did not matter how the bar reached the final locked elbows position—just that it did by any means necessary. Such a practice is dangerous without a "full coverage" safety rack to catch failed attempts of course,[2] and if you could get a decent rack for such a special purpose, you just as well may have procured a bench.
Unless you need to participate in powerlifting competition—or the much more common dick waving competition—a bench is not strictly needed for chest development, period. Although you would do well to at least obtain Olympic rings or bars suitable for dips—parallel, angled, or preferably adjustable—for doing flyes (on the rings) (Figures 2 & 3) and dips (on either), (Figure 4) improvisation leads one down surprising paths. In the past, I have made it a personal challenge to determine how one can get along with only a barbell and nothing more. Dips were always an option though, so I got by with them as one of the few "impurities" of my routine. But with dip bars alone, I felt there was some neglect for the upper chest region.
Enter the "landmine" family of barbell exercises. Such a simple idea. Place one end of a barbell in a corner and load weights on the other end. Now you have something halfway between a lever and a dumbbell. Even though Arnold Schwarzenegger has been witnessed by many doing his famous T-bar rows,[3] (Figure 5) it occurs to few people today to use a barbell in this manner. Now while standing it is possible to target the upper chest—albeit one arm at a time—especially if one uses the appropriate posture to activate the pectorals more than the deltoids. Without the correct posture, it becomes a glorified one-armed overhead press that targets the shoulders, however.[4]
Restriction to a singular one-armed movement may become boring though. Yet there is still another option, and many would know of it—if it weren't all but forgotten. In the 1950s, Olympian weightlifters were rapidly converging on an advanced strategy for an exercise now cast aside since 1972 when it was removed from competition—the clean and press (not the more well known clean and jerk). A strange sight to behold, in the quest for more and more weight, athletes were beginning to bend backwards—not unlike limbo—in order to press the barbell more with the stronger muscles of the chest (while standing!).[5] While it could still be a fairly shoulder dominated movement at times, the potential for it to be both a missing piece in a routine and to activate large swaths of musculature simultaneously—even the abs—is intriguing. Such a full body movement is a rare thing, and the price to safe admission would be much practice. For those seeking a break from monotony, dying on their feet could be the long awaited rebuttal to taking it lying down—on a bench.
Or you could just do pushups.
[1] https://www.youtube.com/watch?v=-6UxzKPixh8
[2] https://www.youtube.com/watch?v=7V13YUxV3u8 *
[3] https://exrx.net/WeightExercises/BackGeneral/LVTBarRowLM †
[4] https://www.exrx.net/WeightExercises/Power/LVOneArmPress
[5] https://www.youtube.com/watch?v=ksm5_Z_HUEY
* Wherein the lifter narrowly misses breaking his ribs from a failed floor press without a safety rack.
† Believe it or not the rounded back form of Arnold for this exercise is possible to do safely.‡ Although, I don't recommend it if you are not healthy and limber or prone to injury.
‡ https://exrx.net/Questions/DangerousExercises#Straight