Except during periods of War or high tension, overland travel via India between the 2 wings was possible. However, after the introduction of a visa and passport requirement in 1952, this became much more expensive and time consuming for most people. Prior to 1955, Pakistanis found travel through India more expensive than it should have been because Pakistan hadn't yet devalued their currency while the Indians insisted on exchanging it at par. Furthermore, the break up of the Indian Railways and the new priorities of both countries meant that the Rail connection was neglected.Thus overland travel was possible but costly and difficult.
For commodities, the Govt. enabled the shipping route between West and East Pakistan to be monopolized by a few Karachi based West Pakistanis who charged high prices. Economically, there was a huge drain on the East Wing because Bengali jute had to pay for development of the West wing.
The air link, via PIA, after 1956, mainly used by bureaucrats and army officers, was very expensive and often detoured via Colombo rather than flying over Indian territory. This was because the Army realized that they would need PIA in the event of hostilities to air lift soldiers (as in fact happened during the 2 Indo-Pak wars) and thus for strategic reasons a longer route needed to be kept operational.
The Indians, whose economy was more dirigiste, worried about smuggling and had little interest or incentive in facilitating overland transport between the 2 wings. However, overland travel was certainly possible except during Wartime or periods of increased tension.