Macro- and microelements, together with trace elements, are essential components of human nutrition. The chemical composition of cereals and soybean can vary depending on geographical origin and cultivation system. This study evaluated the estimated theoretical daily intake (%RDI) of selected macroelements through consumption of 100 g of organic and conventional maize, soybean, and spelt grains. Seed samples were grown and collected at three locations in 2017 year: 1) Maize Research Institute, Zemun Polje (Belgrade): organic and conventional maize (Rumenka hybrid) and organic spelt (Nirvana hybrid); 2) Institute of Field and Vegetable Crops, Novi Sad: organic and conventional soybean (Kaća hybrid); and 3) Nova Varoš: conventional spelt. Determination of macroelements was performed by Inductively Coupled Plasma–Optical Emission Spectrometry (ICP-OES). Concentrations were expressed in µg/g and converted to mg/100 g, and contributions were made to recommended daily intake (RDI). Soybean showed the highest nutritional potential, particularly in Ca (up to 20% RDI), Mg (≈47% RDI), K (≈32% RDI), and S (over 200% RDI). Both soybean and spelt were rich in Fe and Mn, with conventional soybean contributing more than 40% RDI of Fe and spelt exceeding 200% RDI of Mn. Spelt was also a relevant source of Zn, providing more than 200% RDI per 100 g. In contrast, maize generally contributed lower percentages of daily requirements, although it was a notable source of Mg (≈30% RDI) and Zn (≈160–185% RDI). Na content in all grains was very low (<0.5% RDI), which is favorable from a public health perspective. Comparison between organic and conventional samples indicated only minor quantitative differences in mineral composition, without altering overall distribution patterns. These findings suggest that maize, soybean, and spelt significantly contribute to dietary intake of essential elements, with soybean and spelt standing out as particularly valuable sources of minerals in human nutrition.