In "Gun, Germs and Steel", the author notes that domesticated plants can be a lot larger than their wild varieties (I believe they showed a picture of wild wheat which only had ~5 grains of wheat on a stalk).
By the time of the Old Kingdom in Ancient Egypt, was the grain they were growing already quite similar to modern varieties (e.g. would they look reasonably "bushy")? Would most of their other fruit/vegetable crops essentially look "modern"? I'm just trying to understand whether plants had been completely domesticated by that point or whether that happened later.
According to 'Domestication of Plants in the Old World' (Chapter 1), wheat had been domesticated and was shown in pottery as being 'plump'. This was at about 8,500 - 8,100BC which was far before the Egyptians. Further, the wheat and barley are self-pollinating so humans can selectively breed desired strains alongside their wild counterparts (Chapter 3). Due to this, domestication of 'plump' strains could have occurred fairly quickly. On top of all that, the wheat and barley that humans were after were the strains that didn't easily lose their seeds when disturbed (shattered). So, within only a few generations, humans could have accidentally selected cereals that had the gene for non-shattering shells since those would have kept their seeds for later sowing (and eating).
So, I would say that it is likely that what the Egyptians were using would likely look very similar to what we would have seen around 1900.
Only in the last century have humans began industrializing agriculture on a large scale and spending a lot of time breeding hyper-productive plants in large monocultures as well as making hybrid plants. The wheat you see today being grown at large scale might look noticeably different than the wheat you would have seen only 100 years ago.
Here is some of 'Plant Domestication Of The Old World' - https://books.google.com/books/about/Domestication_of_Plants_in_the_Old_World.html?id=1hHSYoqY-AwC&printsec=frontcover&source=kp_read_button#v=onepage&q&f=false
For related reading, here is an article about recent developments in the understanding of how maize was domesticated. The article mentions a paper which I include as well.